Add a manual documenting config file options (#12368)

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diff --git a/changelog.d/12368.doc b/changelog.d/12368.doc
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+Add a manual documenting config file options.
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diff --git a/docs/SUMMARY.md b/docs/SUMMARY.md
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+++ b/docs/SUMMARY.md
@@ -17,6 +17,7 @@
 # Usage
   - [Federation](federate.md)
   - [Configuration](usage/configuration/README.md)
+    - [Configuration Manual](usage/configuration/config_documentation.md) 
     - [Homeserver Sample Config File](usage/configuration/homeserver_sample_config.md)
     - [Logging Sample Config File](usage/configuration/logging_sample_config.md)
     - [Structured Logging](structured_logging.md)
diff --git a/docs/usage/configuration/config_documentation.md b/docs/usage/configuration/config_documentation.md
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+# Configuring Synapse
+
+This is intended as a guide to the Synapse configuration. The behavior of a Synapse instance can be modified 
+through the many configuration settings documented here — each config option is explained, 
+including what the default is, how to change the default and what sort of behaviour the setting governs.
+Also included is an example configuration for each setting. If you don't want to spend a lot of time 
+thinking about options, the config as generated sets sensible defaults for all values. Do note however that the
+database defaults to SQLite, which is not recommended for production usage. You can read more on this subject 
+[here](../../setup/installation.md#using-postgresql).
+
+## Config Conventions
+
+Configuration options that take a time period can be set using a number
+followed by a letter. Letters have the following meanings:
+
+* `s` = second
+* `m` = minute
+* `h` = hour
+* `d` = day
+* `w` = week
+* `y` = year
+
+For example, setting `redaction_retention_period: 5m` would remove redacted
+messages from the database after 5 minutes, rather than 5 months.
+
+### YAML 
+The configuration file is a [YAML](https://yaml.org/) file, which means that certain syntax rules
+apply if you want your config file to be read properly. A few helpful things to know:
+* `#` before any option in the config will comment out that setting and either a default (if available) will 
+   be applied or Synapse will ignore the setting. Thus, in example #1 below, the setting will be read and
+   applied, but in example #2 the setting will not be read and a default will be applied.  
+
+   Example #1:
+   ```yaml
+   pid_file: DATADIR/homeserver.pid
+   ```
+   Example #2:
+   ```yaml
+   #pid_file: DATADIR/homeserver.pid
+   ```
+* Indentation matters! The indentation before a setting
+  will determine whether a given setting is read as part of another
+  setting, or considered on its own. Thus, in example #1, the `enabled` setting
+  is read as a sub-option of the `presence` setting, and will be properly applied.
+  
+  However, the lack of indentation before the `enabled` setting in example #2 means
+  that when reading the config, Synapse will consider both `presence` and `enabled` as
+  different settings. In this case, `presence` has no value, and thus a default applied, and `enabled`
+  is an option that Synapse doesn't recognize and thus ignores.
+  
+  Example #1: 
+  ```yaml
+  presence:
+    enabled: false
+  ```
+  Example #2:
+  ```yaml
+  presence:
+  enabled: false
+  ```
+  In this manual, all top-level settings (ones with no indentation) are identified 
+  at the beginning of their section (i.e. "Config option: `example_setting`") and 
+  the sub-options, if any, are identified and listed in the body of the section. 
+  In addition, each setting has an example of its usage, with the proper indentation
+  shown. 
+
+  
+## Modules
+
+Server admins can expand Synapse's functionality with external modules.
+
+See [here](../../modules/index.md) for more
+documentation on how to configure or create custom modules for Synapse.
+
+
+---
+Config option: `modules`
+
+Use the `module` sub-option to add modules under this option to extend functionality. 
+The `module` setting then has a sub-option, `config`, which can be used to define some configuration
+for the `module`.
+
+Defaults to none.
+
+Example configuration:
+```yaml
+modules:
+  - module: my_super_module.MySuperClass
+    config:
+      do_thing: true
+  - module: my_other_super_module.SomeClass
+    config: {}
+```
+---
+## Server ##
+
+Define your homeserver name and other base options.
+
+---
+Config option: `server_name`
+
+This sets the public-facing domain of the server.
+
+The `server_name` name will appear at the end of usernames and room addresses
+created on your server. For example if the `server_name` was example.com,
+usernames on your server would be in the format `@user:example.com`
+
+In most cases you should avoid using a matrix specific subdomain such as
+matrix.example.com or synapse.example.com as the `server_name` for the same
+reasons you wouldn't use user@email.example.com as your email address.
+See [here](../../delegate.md)
+for information on how to host Synapse on a subdomain while preserving
+a clean `server_name`.
+
+The `server_name` cannot be changed later so it is important to
+configure this correctly before you start Synapse. It should be all
+lowercase and may contain an explicit port.
+
+There is no default for this option. 
+ 
+Example configuration #1:
+```yaml
+server_name: matrix.org 
+```
+Example configuration #2:
+```yaml
+server_name: localhost:8080
+```
+---
+Config option: `pid_file`
+
+When running Synapse as a daemon, the file to store the pid in. Defaults to none.
+
+Example configuration:
+```yaml
+pid_file: DATADIR/homeserver.pid
+```
+---
+Config option: `web_client_location`
+
+The absolute URL to the web client which `/` will redirect to. Defaults to none. 
+
+Example configuration:
+```yaml
+web_client_location: https://riot.example.com/
+```
+---
+Config option: `public_baseurl`
+
+The public-facing base URL that clients use to access this Homeserver (not
+including _matrix/...). This is the same URL a user might enter into the
+'Custom Homeserver URL' field on their client. If you use Synapse with a
+reverse proxy, this should be the URL to reach Synapse via the proxy.
+Otherwise, it should be the URL to reach Synapse's client HTTP listener (see
+'listeners' below).
+
+Defaults to `https://<server_name>/`.
+
+Example configuration:
+```yaml
+public_baseurl: https://example.com/
+```
+---
+Config option: `serve_server_wellknown`
+
+By default, other servers will try to reach our server on port 8448, which can
+be inconvenient in some environments.
+
+Provided `https://<server_name>/` on port 443 is routed to Synapse, this
+option configures Synapse to serve a file at `https://<server_name>/.well-known/matrix/server`. 
+This will tell other servers to send traffic to port 443 instead.
+
+This option currently defaults to false.
+
+See https://matrix-org.github.io/synapse/latest/delegate.html for more
+information.
+
+Example configuration:
+```yaml
+serve_server_wellknown: true
+```
+---
+Config option: `soft_file_limit`
+ 
+Set the soft limit on the number of file descriptors synapse can use.
+Zero is used to indicate synapse should set the soft limit to the hard limit.
+Defaults to 0. 
+
+Example configuration:
+```yaml
+soft_file_limit: 3
+```
+---
+Config option: `presence`
+
+Presence tracking allows users to see the state (e.g online/offline)
+of other local and remote users. Set the `enabled` sub-option to false to  
+disable presence tracking on this homeserver. Defaults to true. 
+This option replaces the previous top-level 'use_presence' option.
+
+Example configuration:
+```yaml
+presence:
+  enabled: false
+```
+---
+Config option: `require_auth_for_profile_requests`
+
+Whether to require authentication to retrieve profile data (avatars, display names) of other 
+users through the client API. Defaults to false. Note that profile data is also available 
+via the federation API, unless `allow_profile_lookup_over_federation` is set to false.
+
+Example configuration:
+```yaml
+require_auth_for_profile_requests: true
+```
+---
+Config option: `limit_profile_requests_to_users_who_share_rooms`
+
+Use this option to require a user to share a room with another user in order
+to retrieve their profile information. Only checked on Client-Server 
+requests. Profile requests from other servers should be checked by the
+requesting server. Defaults to false.
+
+Example configuration: 
+```yaml
+limit_profile_requests_to_users_who_share_rooms: true
+```
+---
+Config option: `include_profile_data_on_invite`
+
+Use this option to prevent a user's profile data from being retrieved and
+displayed in a room until they have joined it. By default, a user's
+profile data is included in an invite event, regardless of the values
+of the above two settings, and whether or not the users share a server.
+Defaults to true.
+
+Example configuration:
+```yaml
+include_profile_data_on_invite: false
+```
+---
+Config option: `allow_public_rooms_without_auth`
+
+If set to true, removes the need for authentication to access the server's
+public rooms directory through the client API, meaning that anyone can
+query the room directory. Defaults to false.
+
+Example configuration:
+```yaml
+allow_public_rooms_without_auth: true
+```
+---
+Config option: `allow_public_rooms_without_auth`
+
+If set to true, allows any other homeserver to fetch the server's public
+rooms directory via federation. Defaults to false.
+
+Example configuration:
+```yaml
+allow_public_rooms_over_federation: true
+```
+---
+Config option: `default_room_version`
+
+The default room version for newly created rooms on this server.
+
+Known room versions are listed [here](https://spec.matrix.org/latest/rooms/#complete-list-of-room-versions)
+
+For example, for room version 1, `default_room_version` should be set
+to "1". 
+
+Currently defaults to "9".
+
+Example configuration:
+```yaml
+default_room_version: "8"
+```
+---
+Config option: `gc_thresholds`
+
+The garbage collection threshold parameters to pass to `gc.set_threshold`, if defined.
+Defaults to none. 
+
+Example configuration:
+```yaml
+gc_thresholds: [700, 10, 10]
+```
+---
+Config option: `gc_min_interval`
+
+The minimum time in seconds between each GC for a generation, regardless of
+the GC thresholds. This ensures that we don't do GC too frequently. A value of `[1s, 10s, 30s]` 
+indicates that a second must pass between consecutive generation 0 GCs, etc.
+
+Defaults to `[1s, 10s, 30s]`.
+
+Example configuration:
+```yaml
+gc_min_interval: [0.5s, 30s, 1m]
+```
+---
+Config option: `filter_timeline_limit`
+
+Set the limit on the returned events in the timeline in the get
+and sync operations. Defaults to 100. A value of -1 means no upper limit.
+
+
+Example configuration:
+```yaml
+filter_timeline_limit: 5000
+```
+---
+Config option: `block_non_admin_invites`
+
+Whether room invites to users on this server should be blocked
+(except those sent by local server admins). Defaults to false.
+
+Example configuration:
+```yaml
+block_non_admin_invites: true
+```
+---
+Config option: `enable_search`
+
+If set to false, new messages will not be indexed for searching and users
+will receive errors when searching for messages. Defaults to true.
+
+Example configuration:
+```yaml
+enable_search: false
+```
+---
+Config option: `ip_range_blacklist`
+ 
+This option prevents outgoing requests from being sent to the specified blacklisted IP address
+CIDR ranges. If this option is not specified then it defaults to private IP
+address ranges (see the example below).
+
+The blacklist applies to the outbound requests for federation, identity servers,
+push servers, and for checking key validity for third-party invite events.
+
+(0.0.0.0 and :: are always blacklisted, whether or not they are explicitly
+listed here, since they correspond to unroutable addresses.)
+
+This option replaces `federation_ip_range_blacklist` in Synapse v1.25.0.
+
+Note: The value is ignored when an HTTP proxy is in use.
+
+Example configuration:
+```yaml
+ip_range_blacklist:
+  - '127.0.0.0/8'
+  - '10.0.0.0/8'
+  - '172.16.0.0/12'
+  - '192.168.0.0/16'
+  - '100.64.0.0/10'
+  - '192.0.0.0/24'
+  - '169.254.0.0/16'
+  - '192.88.99.0/24'
+  - '198.18.0.0/15'
+  - '192.0.2.0/24'
+  - '198.51.100.0/24'
+  - '203.0.113.0/24'
+  - '224.0.0.0/4'
+  - '::1/128'
+  - 'fe80::/10'
+  - 'fc00::/7'
+  - '2001:db8::/32'
+  - 'ff00::/8'
+  - 'fec0::/10'
+```
+---
+Config option: `ip_range_whitelist`
+
+List of IP address CIDR ranges that should be allowed for federation,
+identity servers, push servers, and for checking key validity for
+third-party invite events. This is useful for specifying exceptions to
+wide-ranging blacklisted target IP ranges - e.g. for communication with
+a push server only visible in your network.
+
+This whitelist overrides `ip_range_blacklist` and defaults to an empty
+list.
+
+Example configuration:
+```yaml
+ip_range_whitelist:
+   - '192.168.1.1'
+```
+---
+Config option: `listeners`
+
+List of ports that Synapse should listen on, their purpose and their
+configuration.
+
+Sub-options for each listener include:
+
+* `port`: the TCP port to bind to. 
+
+* `bind_addresses`: a list of local addresses to listen on. The default is
+       'all local interfaces'.
+
+* `type`: the type of listener. Normally `http`, but other valid options are:
+    
+   * `manhole`: (see the docs [here](../../manhole.md)),
+
+   * `metrics`: (see the docs [here](../../metrics-howto.md)),
+
+   * `replication`: (see the docs [here](../../workers.md)).
+
+* `tls`: set to true to enable TLS for this listener. Will use the TLS key/cert specified in tls_private_key_path / tls_certificate_path.
+
+* `x_forwarded`: Only valid for an 'http' listener. Set to true to use the X-Forwarded-For header as the client IP. Useful when Synapse is
+   behind a reverse-proxy.
+
+* `resources`: Only valid for an 'http' listener. A list of resources to host
+   on this port. Sub-options for each resource are:
+
+   * `names`: a list of names of HTTP resources. See below for a list of valid resource names.
+
+   * `compress`: set to true to enable HTTP compression for this resource.
+
+* `additional_resources`: Only valid for an 'http' listener. A map of
+   additional endpoints which should be loaded via dynamic modules.
+
+Valid resource names are:
+
+* `client`: the client-server API (/_matrix/client), and the synapse admin API (/_synapse/admin). Also implies 'media' and 'static'.
+
+* `consent`: user consent forms (/_matrix/consent). See [here](../../consent_tracking.md) for more.
+
+* `federation`: the server-server API (/_matrix/federation). Also implies `media`, `keys`, `openid`
+
+* `keys`: the key discovery API (/_matrix/keys).
+
+* `media`: the media API (/_matrix/media).
+
+* `metrics`: the metrics interface. See [here](../../metrics-howto.md).
+
+* `openid`: OpenID authentication. See [here](../../openid.md).
+
+* `replication`: the HTTP replication API (/_synapse/replication). See [here](../../workers.md).
+
+* `static`: static resources under synapse/static (/_matrix/static). (Mostly useful for 'fallback authentication'.)
+
+Example configuration #1:
+```yaml
+listeners:
+  # TLS-enabled listener: for when matrix traffic is sent directly to synapse.
+  #
+  # (Note that you will also need to give Synapse a TLS key and certificate: see the TLS section
+  # below.)
+  #
+  - port: 8448
+    type: http
+    tls: true
+    resources:
+      - names: [client, federation]
+```
+Example configuration #2:
+```yaml
+listeners:
+  # Unsecure HTTP listener: for when matrix traffic passes through a reverse proxy
+  # that unwraps TLS.
+  #
+  # If you plan to use a reverse proxy, please see
+  # https://matrix-org.github.io/synapse/latest/reverse_proxy.html.
+  #
+  - port: 8008
+    tls: false
+    type: http
+    x_forwarded: true
+    bind_addresses: ['::1', '127.0.0.1']
+
+    resources:
+      - names: [client, federation]
+        compress: false
+
+    # example additional_resources:
+    additional_resources:
+      "/_matrix/my/custom/endpoint":
+        module: my_module.CustomRequestHandler
+        config: {}
+
+  # Turn on the twisted ssh manhole service on localhost on the given
+  # port.
+  - port: 9000
+    bind_addresses: ['::1', '127.0.0.1']
+    type: manhole
+```
+---
+Config option: `manhole_settings`
+
+Connection settings for the manhole. You can find more information
+on the manhole [here](../../manhole.md). Manhole sub-options include:
+* `username` : the username for the manhole. This defaults to 'matrix'.
+* `password`: The password for the manhole. This defaults to 'rabbithole'.
+* `ssh_priv_key_path` and `ssh_pub_key_path`: The private and public SSH key pair used to encrypt the manhole traffic.
+  If these are left unset, then hardcoded and non-secret keys are used,
+  which could allow traffic to be intercepted if sent over a public network.
+
+Example configuration:
+```yaml
+manhole_settings:
+  username: manhole
+  password: mypassword
+  ssh_priv_key_path: CONFDIR/id_rsa
+  ssh_pub_key_path: CONFDIR/id_rsa.pub
+```
+---
+Config option: `dummy_events_threshold`
+
+Forward extremities can build up in a room due to networking delays between
+homeservers. Once this happens in a large room, calculation of the state of
+that room can become quite expensive. To mitigate this, once the number of
+forward extremities reaches a given threshold, Synapse will send an
+`org.matrix.dummy_event` event, which will reduce the forward extremities
+in the room.
+
+This setting defines the threshold (i.e. number of forward extremities in the room) at which dummy events are sent. 
+The default value is 10.
+
+Example configuration:
+```yaml
+dummy_events_threshold: 5
+```
+---
+## Homeserver blocking ##
+Useful options for Synapse admins.
+
+---
+
+Config option: `admin_contact`
+
+How to reach the server admin, used in `ResourceLimitError`. Defaults to none. 
+
+Example configuration:
+```yaml
+admin_contact: 'mailto:admin@server.com'
+```
+---
+Config option: `hs_disabled` and `hs_disabled_message`
+
+Blocks users from connecting to the homeserver and provides a human-readable reason
+why the connection was blocked. Defaults to false. 
+
+Example configuration:
+```yaml
+hs_disabled: true
+hs_disabled_message: 'Reason for why the HS is blocked'
+```
+---
+Config option: `limit_usage_by_mau`
+
+This option disables/enables monthly active user blocking. Used in cases where the admin or 
+server owner wants to limit to the number of monthly active users. When enabled and a limit is 
+reached the server returns a `ResourceLimitError` with error type `Codes.RESOURCE_LIMIT_EXCEEDED`.
+Defaults to false. If this is enabled, a value for `max_mau_value` must also be set.
+
+Example configuration:
+```yaml
+limit_usage_by_mau: true 
+```
+---
+Config option: `max_mau_value`
+
+This option sets the hard limit of monthly active users above which the server will start 
+blocking user actions if `limit_usage_by_mau` is enabled. Defaults to 0.  
+
+Example configuration:
+```yaml
+max_mau_value: 50
+```
+---
+Config option: `mau_trial_days`
+
+The option `mau_trial_days` is a means to add a grace period for active users. It
+means that users must be active for the specified number of days before they
+can be considered active and guards against the case where lots of users
+sign up in a short space of time never to return after their initial
+session. Defaults to 0. 
+
+Example configuration:
+```yaml
+mau_trial_days: 5
+```
+---
+Config option: `mau_limit_alerting`
+
+The option `mau_limit_alerting` is a means of limiting client-side alerting
+should the mau limit be reached. This is useful for small instances
+where the admin has 5 mau seats (say) for 5 specific people and no
+interest increasing the mau limit further. Defaults to true, which
+means that alerting is enabled.
+
+Example configuration:
+```yaml
+mau_limit_alerting: false
+```
+---
+Config option: `mau_stats_only`
+
+If enabled, the metrics for the number of monthly active users will
+be populated, however no one will be limited based on these numbers. If `limit_usage_by_mau`
+is true, this is implied to be true. Defaults to false. 
+
+Example configuration:
+```yaml
+mau_stats_only: true
+```
+---
+Config option: `mau_limit_reserved_threepids`
+
+Sometimes the server admin will want to ensure certain accounts are
+never blocked by mau checking. These accounts are specified by this option.
+Defaults to none. Add accounts by specifying the `medium` and `address` of the
+reserved threepid (3rd party identifier).
+
+Example configuration:
+```yaml
+mau_limit_reserved_threepids:
+  - medium: 'email'
+    address: 'reserved_user@example.com'
+```
+---
+Config option: `server_context`
+
+This option is used by phonehome stats to group together related servers.
+Defaults to none. 
+
+Example configuration:
+```yaml
+server_context: context
+```
+---
+Config option: `limit_remote_rooms`
+
+When this option is enabled, the room "complexity" will be checked before a user
+joins a new remote room. If it is above the complexity limit, the server will
+disallow joining, or will instantly leave. This is useful for homeservers that are
+resource-constrained. Options for this setting include:
+* `enabled`: whether this check is enabled. Defaults to false.
+* `complexity`: the limit above which rooms cannot be joined. The default is 1.0.
+* `complexity_error`: override the error which is returned when the room is too complex with a
+   custom message. 
+* `admins_can_join`: allow server admins to join complex rooms. Default is false.
+
+Room complexity is an arbitrary measure based on factors such as the number of
+users in the room. 
+
+Example configuration:
+```yaml
+limit_remote_rooms:
+  enabled: true
+  complexity: 0.5
+  complexity_error: "I can't let you do that, Dave."
+  admins_can_join: true
+```
+---
+Config option: `require_membership_for_aliases`
+
+Whether to require a user to be in the room to add an alias to it.
+Defaults to true.
+
+Example configuration:
+```yaml
+require_membership_for_aliases: false
+```
+---
+Config option: `allow_per_room_profiles`
+
+Whether to allow per-room membership profiles through the sending of membership
+events with profile information that differs from the target's global profile.
+Defaults to true.
+
+Example configuration:
+```yaml
+allow_per_room_profiles: false
+```
+---
+Config option: `max_avatar_size`
+
+The largest permissible file size in bytes for a user avatar. Defaults to no restriction.
+Use M for MB and K for KB. 
+
+Note that user avatar changes will not work if this is set without using Synapse's media repository.
+
+Example configuration:
+```yaml
+max_avatar_size: 10M
+```
+---
+Config option: `allowed_avatar_mimetypes`
+
+The MIME types allowed for user avatars. Defaults to no restriction.
+
+Note that user avatar changes will not work if this is set without
+using Synapse's media repository.
+
+Example configuration:
+```yaml
+allowed_avatar_mimetypes: ["image/png", "image/jpeg", "image/gif"]
+```
+---
+Config option: `redaction_retention_period`
+
+How long to keep redacted events in unredacted form in the database. After
+this period redacted events get replaced with their redacted form in the DB.
+
+Defaults to `7d`. Set to `null` to disable.
+
+Example configuration:
+```yaml
+redaction_retention_period: 28d
+```
+---
+Config option: `user_ips_max_age` 
+
+How long to track users' last seen time and IPs in the database.
+
+Defaults to `28d`. Set to `null` to disable clearing out of old rows.
+
+Example configuration:
+```yaml
+user_ips_max_age: 14d
+```
+---
+Config option: `request_token_inhibit_3pid_errors`
+
+Inhibits the `/requestToken` endpoints from returning an error that might leak
+information about whether an e-mail address is in use or not on this
+homeserver. Defaults to false. 
+Note that for some endpoints the error situation is the e-mail already being
+used, and for others the error is entering the e-mail being unused.
+If this option is enabled, instead of returning an error, these endpoints will
+act as if no error happened and return a fake session ID ('sid') to clients.
+
+Example configuration:
+```yaml
+request_token_inhibit_3pid_errors: true
+```
+---
+Config option: `next_link_domain_whitelist`
+
+A list of domains that the domain portion of `next_link` parameters
+must match.
+
+This parameter is optionally provided by clients while requesting
+validation of an email or phone number, and maps to a link that
+users will be automatically redirected to after validation
+succeeds. Clients can make use this parameter to aid the validation
+process.
+
+The whitelist is applied whether the homeserver or an identity server is handling validation.
+
+The default value is no whitelist functionality; all domains are
+allowed. Setting this value to an empty list will instead disallow
+all domains.
+
+Example configuration:
+```yaml
+next_link_domain_whitelist: ["matrix.org"]
+```
+---
+Config option: `templates` and `custom_template_directory`
+
+These options define templates to use when generating email or HTML page contents.
+The `custom_template_directory` determines which directory Synapse will try to 
+find template files in to use to generate email or HTML page contents.
+If not set, or a file is not found within the template directory, a default 
+template from within the Synapse package will be used.
+
+See [here](../../templates.md) for more
+information about using custom templates.
+
+Example configuration:
+```yaml
+templates:
+  custom_template_directory: /path/to/custom/templates/
+```
+---
+Config option: `retention`
+
+This option and the associated options determine message retention policy at the
+server level.
+
+Room admins and mods can define a retention period for their rooms using the
+`m.room.retention` state event, and server admins can cap this period by setting
+the `allowed_lifetime_min` and `allowed_lifetime_max` config options.
+
+If this feature is enabled, Synapse will regularly look for and purge events
+which are older than the room's maximum retention period. Synapse will also
+filter events received over federation so that events that should have been 
+purged are ignored and not stored again. 
+
+The message retention policies feature is disabled by default.
+
+This setting has the following sub-options:
+* `default_policy`: Default retention policy. If set, Synapse will apply it to rooms that lack the
+   'm.room.retention' state event. This option is further specified by the 
+   `min_lifetime` and `max_lifetime` sub-options associated with it. Note that the 
+    value of `min_lifetime` doesn't matter much because Synapse doesn't take it into account yet. 
+
+* `allowed_lifetime_min` and `allowed_lifetime_max`: Retention policy limits. If 
+   set, and the state of a room contains a `m.room.retention` event in its state 
+   which contains a `min_lifetime` or a `max_lifetime` that's out of these bounds,
+   Synapse will cap the room's policy to these limits when running purge jobs.
+
+* `purge_jobs` and the associated `shortest_max_lifetime` and `longest_max_lifetime` sub-options:
+   Server admins can define the settings of the background jobs purging the
+   events whose lifetime has expired under the `purge_jobs` section.
+   
+  If no configuration is provided for this option, a single job will be set up to delete
+  expired events in every room daily.
+
+  Each job's configuration defines which range of message lifetimes the job
+  takes care of. For example, if `shortest_max_lifetime` is '2d' and
+  `longest_max_lifetime` is '3d', the job will handle purging expired events in
+  rooms whose state defines a `max_lifetime` that's both higher than 2 days, and
+  lower than or equal to 3 days. Both the minimum and the maximum value of a
+  range are optional, e.g. a job with no `shortest_max_lifetime` and a
+  `longest_max_lifetime` of '3d' will handle every room with a retention policy
+  whose `max_lifetime` is lower than or equal to three days.
+  
+  The rationale for this per-job configuration is that some rooms might have a
+  retention policy with a low `max_lifetime`, where history needs to be purged
+  of outdated messages on a more frequent basis than for the rest of the rooms
+  (e.g. every 12h), but not want that purge to be performed by a job that's
+  iterating over every room it knows, which could be heavy on the server.
+
+  If any purge job is configured, it is strongly recommended to have at least
+  a single job with neither `shortest_max_lifetime` nor `longest_max_lifetime`
+  set, or one job without `shortest_max_lifetime` and one job without
+  `longest_max_lifetime` set. Otherwise some rooms might be ignored, even if
+  `allowed_lifetime_min` and `allowed_lifetime_max` are set, because capping a
+  room's policy to these values is done after the policies are retrieved from
+  Synapse's database (which is done using the range specified in a purge job's
+  configuration).
+
+Example configuration:
+```yaml
+retention:
+  enabled: true
+  default_policy:
+    min_lifetime: 1d
+    max_lifetime: 1y
+  allowed_lifetime_min: 1d
+  allowed_lifetime_max: 1y
+  purge_jobs:
+    - longest_max_lifetime: 3d
+      interval: 12h
+    - shortest_max_lifetime: 3d
+      interval: 1d  
+```
+---
+## TLS ##
+
+Options related to TLS.
+
+---
+Config option: `tls_certificate_path`
+
+This option specifies a PEM-encoded X509 certificate for TLS.
+This certificate, as of Synapse 1.0, will need to be a valid and verifiable
+certificate, signed by a recognised Certificate Authority. Defaults to none. 
+
+Be sure to use a `.pem` file that includes the full certificate chain including
+any intermediate certificates (for instance, if using certbot, use
+`fullchain.pem` as your certificate, not `cert.pem`). 
+
+Example configuration:
+```yaml
+tls_certificate_path: "CONFDIR/SERVERNAME.tls.crt"
+```
+---
+Config option: `tls_private_key_path`
+
+PEM-encoded private key for TLS. Defaults to none. 
+
+Example configuration:
+```yaml
+tls_private_key_path: "CONFDIR/SERVERNAME.tls.key"
+```
+---
+Config option: `federation_verify_certificates`
+Whether to verify TLS server certificates for outbound federation requests.
+
+Defaults to true. To disable certificate verification, set the option to false.
+
+Example configuration:
+```yaml
+federation_verify_certificates: false
+```
+---
+Config option: `federation_client_minimum_tls_version`
+
+The minimum TLS version that will be used for outbound federation requests.
+
+Defaults to `1`. Configurable to `1`, `1.1`, `1.2`, or `1.3`. Note
+that setting this value higher than `1.2` will prevent federation to most
+of the public Matrix network: only configure it to `1.3` if you have an
+entirely private federation setup and you can ensure TLS 1.3 support.
+
+Example configuration:
+```yaml
+federation_client_minimum_tls_version: 1.2
+```
+---
+Config option: `federation_certificate_verification_whitelist`
+
+Skip federation certificate verification on a given whitelist
+of domains.
+
+This setting should only be used in very specific cases, such as
+federation over Tor hidden services and similar. For private networks
+of homeservers, you likely want to use a private CA instead.
+
+Only effective if `federation_verify_certicates` is `true`.
+
+Example configuration:
+```yaml
+federation_certificate_verification_whitelist:
+  - lon.example.com
+  - "*.domain.com"
+  - "*.onion"
+```
+---
+Config option: `federation_custom_ca_list`
+
+List of custom certificate authorities for federation traffic.
+
+This setting should only normally be used within a private network of
+homeservers.
+
+Note that this list will replace those that are provided by your
+operating environment. Certificates must be in PEM format.
+
+Example configuration:
+```yaml
+federation_custom_ca_list:
+  - myCA1.pem
+  - myCA2.pem
+  - myCA3.pem
+```
+---
+## Federation ##
+
+Options related to federation.
+
+---
+Config option: `federation_domain_whitelist`
+
+Restrict federation to the given whitelist of domains.
+N.B. we recommend also firewalling your federation listener to limit
+inbound federation traffic as early as possible, rather than relying
+purely on this application-layer restriction.  If not specified, the
+default is to whitelist everything.
+
+Example configuration:
+```yaml
+federation_domain_whitelist:
+  - lon.example.com
+  - nyc.example.com
+  - syd.example.com
+```
+---
+Config option: `federation_metrics_domains`
+
+Report prometheus metrics on the age of PDUs being sent to and received from
+the given domains. This can be used to give an idea of "delay" on inbound
+and outbound federation, though be aware that any delay can be due to problems
+at either end or with the intermediate network.
+
+By default, no domains are monitored in this way.
+
+Example configuration:
+```yaml
+federation_metrics_domains:
+  - matrix.org
+  - example.com
+```
+---
+Config option: `allow_profile_lookup_over_federation`
+
+Set to false to disable profile lookup over federation. By default, the
+Federation API allows other homeservers to obtain profile data of any user
+on this homeserver.
+
+Example configuration:
+```yaml
+allow_profile_lookup_over_federation: false
+```
+---
+Config option: `allow_device_name_lookup_over_federation`
+
+Set this option to false to disable device display name lookup over federation. By default, the
+Federation API allows other homeservers to obtain device display names of any user
+on this homeserver.
+
+Example configuration:
+```yaml
+allow_device_name_lookup_over_federation: false
+```
+---
+## Caching ##
+
+Options related to caching
+
+---
+Config option: `event_cache_size`
+
+The number of events to cache in memory. Not affected by
+`caches.global_factor`. Defaults to 10K.
+
+Example configuration:
+```yaml
+event_cache_size: 15K
+```
+---
+Config option: `cache` and associated values
+
+A cache 'factor' is a multiplier that can be applied to each of
+Synapse's caches in order to increase or decrease the maximum
+number of entries that can be stored.
+
+Caching can be configured through the following sub-options:
+
+* `global_factor`: Controls the global cache factor, which is the default cache factor
+  for all caches if a specific factor for that cache is not otherwise
+  set.
+
+  This can also be set by the `SYNAPSE_CACHE_FACTOR` environment
+  variable. Setting by environment variable takes priority over
+  setting through the config file.
+  
+  Defaults to 0.5, which will halve the size of all caches.
+
+* `per_cache_factors`: A dictionary of cache name to cache factor for that individual
+   cache. Overrides the global cache factor for a given cache.
+  
+   These can also be set through environment variables comprised
+   of `SYNAPSE_CACHE_FACTOR_` + the name of the cache in capital
+   letters and underscores. Setting by environment variable
+   takes priority over setting through the config file.
+   Ex. `SYNAPSE_CACHE_FACTOR_GET_USERS_WHO_SHARE_ROOM_WITH_USER=2.0`
+  
+   Some caches have '*' and other characters that are not
+   alphanumeric or underscores. These caches can be named with or
+   without the special characters stripped. For example, to specify
+   the cache factor for `*stateGroupCache*` via an environment
+   variable would be `SYNAPSE_CACHE_FACTOR_STATEGROUPCACHE=2.0`.
+ 
+* `expire_caches`: Controls whether cache entries are evicted after a specified time
+   period. Defaults to true. Set to false to disable this feature. Note that never expiring
+   caches may result in excessive memory usage. 
+
+* `cache_entry_ttl`: If `expire_caches` is enabled, this flag controls how long an entry can
+  be in a cache without having been accessed before being evicted.
+  Defaults to 30m. 
+
+* `sync_response_cache_duration`: Controls how long the results of a /sync request are
+  cached for after a successful response is returned. A higher duration can help clients
+  with intermittent connections, at the cost of higher memory usage.
+  By default, this is zero, which means that sync responses are not cached
+  at all.
+
+
+Example configuration:
+```yaml
+caches:
+  global_factor: 1.0
+  per_cache_factors:
+    get_users_who_share_room_with_user: 2.0
+  expire_caches: false
+  sync_response_cache_duration: 2m
+```
+---
+## Database ##
+Config options related to database settings.
+
+---
+Config option: `database`
+
+The `database` setting defines the database that synapse uses to store all of
+its data.
+
+Associated sub-options:
+
+* `name`: this option specifies the database engine to use: either `sqlite3` (for SQLite)
+  or `psycopg2` (for PostgreSQL). If no name is specified Synapse will default to SQLite. 
+
+* `txn_limit` gives the maximum number of transactions to run per connection
+  before reconnecting. Defaults to 0, which means no limit.
+
+* `allow_unsafe_locale` is an option specific to Postgres. Under the default behavior, Synapse will refuse to
+  start if the postgres db is set to a non-C locale. You can override this behavior (which is *not* recommended)
+  by setting `allow_unsafe_locale` to true. Note that doing so may corrupt your database. You can find more information
+  [here](../../postgres.md#fixing-incorrect-collate-or-ctype) and [here](https://wiki.postgresql.org/wiki/Locale_data_changes).
+
+* `args` gives options which are passed through to the database engine,
+  except for options starting with `cp_`, which are used to configure the Twisted
+  connection pool. For a reference to valid arguments, see:
+    * for [sqlite](https://docs.python.org/3/library/sqlite3.html#sqlite3.connect)
+    * for [postgres](https://www.postgresql.org/docs/current/libpq-connect.html#LIBPQ-PARAMKEYWORDS)
+    * for [the connection pool](https://twistedmatrix.com/documents/current/api/twisted.enterprise.adbapi.ConnectionPool.html#__init__)
+
+For more information on using Synapse with Postgres,
+see [here](../../postgres.md).
+
+Example SQLite configuration:
+```
+database:
+  name: sqlite3
+  args:
+    database: /path/to/homeserver.db
+```
+
+Example Postgres configuration:
+```
+database:
+  name: psycopg2
+  txn_limit: 10000
+  args:
+    user: synapse_user
+    password: secretpassword
+    database: synapse
+    host: localhost
+    port: 5432
+    cp_min: 5
+    cp_max: 10
+```
+---
+## Logging ##
+Config options related to logging. 
+
+---
+Config option: `log_config`
+
+This option specifies a yaml python logging config file as described [here](https://docs.python.org/3.7/library/logging.config.html#configuration-dictionary-schema).
+
+Example configuration:
+```yaml
+log_config: "CONFDIR/SERVERNAME.log.config"
+```
+---
+## Ratelimiting ##
+Options related to ratelimiting in Synapse. 
+
+Each ratelimiting configuration is made of two parameters:
+   - `per_second`: number of requests a client can send per second.
+   - `burst_count`: number of requests a client can send before being throttled.
+---
+Config option: `rc_message`
+
+
+Ratelimiting settings for client messaging.
+   
+This is a ratelimiting option for messages that ratelimits sending based on the account the client
+is using. It defaults to: `per_second: 0.2`, `burst_count: 10`.
+
+Example configuration:
+```yaml
+rc_message:
+  per_second: 0.5
+  burst_count: 15
+```
+---
+Config option: `rc_registration`
+
+This option ratelimits registration requests based on the client's IP address.
+It defaults to `per_second: 0.17`, `burst_count: 3`. 
+
+Example configuration:
+```yaml
+rc_registration:
+  per_second: 0.15
+  burst_count: 2
+```
+---
+Config option: `rc_registration_token_validity`
+
+This option checks the validity of registration tokens that ratelimits requests based on 
+the client's IP address.
+Defaults to `per_second: 0.1`, `burst_count: 5`.
+
+Example configuration:
+```yaml
+rc_registration_token_validity:
+  per_second: 0.3
+  burst_count: 6
+```   
+---
+Config option: `rc_login`
+
+This option specifies several limits for login:
+* `address` ratelimits login requests based on the client's IP
+      address. Defaults to `per_second: 0.17`, `burst_count: 3`.
+    
+* `account` ratelimits login requests based on the account the
+  client is attempting to log into. Defaults to `per_second: 0.17`,
+  `burst_count: 3`.
+    
+* `failted_attempts` ratelimits login requests based on the account the
+  client is attempting to log into, based on the amount of failed login
+  attempts for this account. Defaults to `per_second: 0.17`, `burst_count: 3`.
+
+Example configuration:
+```yaml
+rc_login:
+  address:
+    per_second: 0.15
+    burst_count: 5
+  account:
+    per_second: 0.18
+    burst_count: 4
+  failed_attempts:
+    per_second: 0.19
+    burst_count: 7
+```
+---
+Config option: `rc_admin_redaction`
+
+This option sets ratelimiting redactions by room admins. If this is not explicitly 
+set then it uses the same ratelimiting as per `rc_message`. This is useful
+to allow room admins to deal with abuse quickly. 
+
+Example configuration:
+```yaml
+rc_admin_redaction:
+  per_second: 1
+  burst_count: 50
+```
+---
+Config option: `rc_joins`
+
+This option allows for ratelimiting number of rooms a user can join. This setting has the following sub-options:
+
+* `local`: ratelimits when users are joining rooms the server is already in. 
+   Defaults to `per_second: 0.1`, `burst_count: 10`.
+
+* `remote`: ratelimits when users are trying to join rooms not on the server (which
+  can be more computationally expensive than restricting locally). Defaults to
+  `per_second: 0.01`, `burst_count: 10` 
+
+Example configuration:
+```yaml
+rc_joins:
+  local:
+    per_second: 0.2
+    burst_count: 15
+  remote:
+    per_second: 0.03
+    burst_count: 12
+```
+---
+Config option: `rc_3pid_validation`
+
+This option ratelimits how often a user or IP can attempt to validate a 3PID.
+Defaults to `per_second: 0.003`, `burst_count: 5`.
+
+Example configuration:
+```yaml
+rc_3pid_validation:
+  per_second: 0.003
+  burst_count: 5
+```
+---
+Config option: `rc_invites`
+
+This option sets ratelimiting how often invites can be sent in a room or to a 
+specific user. `per_room` defaults to `per_second: 0.3`, `burst_count: 10` and
+`per_user` defaults to `per_second: 0.003`, `burst_count: 5`. 
+
+Example configuration:
+```yaml
+rc_invites:
+  per_room:
+    per_second: 0.5
+    burst_count: 5
+  per_user:
+    per_second: 0.004
+    burst_count: 3
+```
+---
+Config option: `rc_third_party_invite`
+
+This option ratelimits 3PID invites (i.e. invites sent to a third-party ID
+such as an email address or a phone number) based on the account that's
+sending the invite. Defaults to `per_second: 0.2`, `burst_count: 10`.
+
+Example configuration:
+```yaml
+rc_third_party_invite:
+  per_second: 0.2
+  burst_count: 10
+```
+---
+Config option: `rc_federation`
+
+Defines limits on federation requests. 
+
+The `rc_federation` configuration has the following sub-options:
+* `window_size`: window size in milliseconds. Defaults to 1000.
+* `sleep_limit`: number of federation requests from a single server in
+   a window before the server will delay processing the request. Defaults to 10.
+* `sleep_delay`: duration in milliseconds to delay processing events
+   from remote servers by if they go over the sleep limit. Defaults to 500.
+* `reject_limit`: maximum number of concurrent federation requests
+   allowed from a single server. Defaults to 50.
+* `concurrent`: number of federation requests to concurrently process
+   from a single server. Defaults to 3.
+
+Example configuration:
+```yaml
+rc_federation:
+  window_size: 750
+  sleep_limit: 15
+  sleep_delay: 400
+  reject_limit: 40
+  concurrent: 5
+```
+---
+Config option: `federation_rr_transactions_per_room_per_second`
+
+Sets outgoing federation transaction frequency for sending read-receipts,
+per-room.
+
+If we end up trying to send out more read-receipts, they will get buffered up
+into fewer transactions. Defaults to 50. 
+
+Example configuration:
+```yaml
+federation_rr_transactions_per_room_per_second: 40
+```
+---
+## Media Store ##
+Config options relating to Synapse media store.
+
+---
+Config option: `enable_media_repo` 
+
+Enable the media store service in the Synapse master. Defaults to true. 
+Set to false if you are using a separate media store worker.
+
+Example configuration:
+```yaml
+enable_media_repo: false
+```
+---
+Config option: `media_store_path`
+
+Directory where uploaded images and attachments are stored.
+
+Example configuration:
+```yaml
+media_store_path: "DATADIR/media_store"
+```
+---
+Config option: `media_storage_providers`
+
+Media storage providers allow media to be stored in different
+locations. Defaults to none. Associated sub-options are:
+* `module`: type of resource, e.g. `file_system`.
+* `store_local`: whether to store newly uploaded local files
+* `store_remote`: whether to store newly downloaded local files
+* `store_synchronous`: whether to wait for successful storage for local uploads
+* `config`: sets a path to the resource through the `directory` option 
+
+Example configuration:
+```yaml
+media_storage_providers:
+  - module: file_system
+    store_local: false
+    store_remote: false
+    store_synchronous: false
+    config:
+       directory: /mnt/some/other/directory
+```
+---
+Config option: `max_upload_size`
+
+The largest allowed upload size in bytes.
+
+If you are using a reverse proxy you may also need to set this value in
+your reverse proxy's config. Defaults to 50M. Notably Nginx has a small max body size by default.
+See [here](../../reverse_proxy.md) for more on using a reverse proxy with Synapse. 
+
+Example configuration:
+```yaml
+max_upload_size: 60M
+```
+---
+Config option: `max_image_pixels`
+
+Maximum number of pixels that will be thumbnailed. Defaults to 32M.
+
+Example configuration:
+```yaml
+max_image_pixels: 35M
+```
+---
+Config option: `dynamic_thumbnails`
+
+Whether to generate new thumbnails on the fly to precisely match
+the resolution requested by the client. If true then whenever
+a new resolution is requested by the client the server will
+generate a new thumbnail. If false the server will pick a thumbnail
+from a precalculated list. Defaults to false. 
+
+Example configuration:
+```yaml
+dynamic_thumbnails: true
+```
+---
+Config option: `thumbnail_sizes`  
+
+List of thumbnails to precalculate when an image is uploaded. Associated sub-options are:
+* `width`
+* `height`
+* `method`: i.e. `crop`, `scale`, etc.
+
+Example configuration:
+```yaml
+thumbnail_sizes:
+  - width: 32
+    height: 32
+    method: crop
+  - width: 96
+    height: 96
+    method: crop
+  - width: 320
+    height: 240
+    method: scale
+  - width: 640
+    height: 480
+    method: scale
+  - width: 800
+    height: 600
+    method: scale
+```
+Config option: `url_preview_enabled`
+
+This setting determines whether the preview URL API is enabled.
+It is disabled by default. Set to true to enable. If enabled you must specify a
+`url_preview_ip_range_blacklist` blacklist.
+
+Example configuration:
+```yaml
+url_preview_enabled: true
+```
+---
+Config option: `url_preview_ip_range_blacklist`
+
+List of IP address CIDR ranges that the URL preview spider is denied
+from accessing.  There are no defaults: you must explicitly
+specify a list for URL previewing to work.  You should specify any
+internal services in your network that you do not want synapse to try
+to connect to, otherwise anyone in any Matrix room could cause your
+synapse to issue arbitrary GET requests to your internal services,
+causing serious security issues.
+
+(0.0.0.0 and :: are always blacklisted, whether or not they are explicitly
+listed here, since they correspond to unroutable addresses.)
+
+This must be specified if `url_preview_enabled` is set. It is recommended that
+you use the following example list as a starting point.
+
+Note: The value is ignored when an HTTP proxy is in use.
+
+Example configuration:
+```yaml
+url_preview_ip_range_blacklist:
+  - '127.0.0.0/8'
+  - '10.0.0.0/8'
+  - '172.16.0.0/12'
+  - '192.168.0.0/16'
+  - '100.64.0.0/10'
+  - '192.0.0.0/24'
+  - '169.254.0.0/16'
+  - '192.88.99.0/24'
+  - '198.18.0.0/15'
+  - '192.0.2.0/24'
+  - '198.51.100.0/24'
+  - '203.0.113.0/24'
+  - '224.0.0.0/4'
+  - '::1/128'
+  - 'fe80::/10'
+  - 'fc00::/7'
+  - '2001:db8::/32'
+  - 'ff00::/8'
+  - 'fec0::/10'
+```
+----
+Config option: `url_preview_ip_range_whitelist`
+
+This option sets a list of IP address CIDR ranges that the URL preview spider is allowed
+to access even if they are specified in `url_preview_ip_range_blacklist`.
+This is useful for specifying exceptions to wide-ranging blacklisted
+target IP ranges - e.g. for enabling URL previews for a specific private
+website only visible in your network. Defaults to none. 
+
+Example configuration:
+```yaml
+url_preview_ip_range_whitelist:
+   - '192.168.1.1'
+```
+---
+Config option: `url_preview_url_blacklist`
+
+Optional list of URL matches that the URL preview spider is
+denied from accessing.  You should use `url_preview_ip_range_blacklist`
+in preference to this, otherwise someone could define a public DNS
+entry that points to a private IP address and circumvent the blacklist.
+This is more useful if you know there is an entire shape of URL that
+you know that will never want synapse to try to spider.
+
+Each list entry is a dictionary of url component attributes as returned
+by urlparse.urlsplit as applied to the absolute form of the URL.  See 
+[here](https://docs.python.org/2/library/urlparse.html#urlparse.urlsplit) for more
+information. Some examples are:
+
+* `username`
+* `netloc`
+* `scheme`
+* `path`
+
+The values of the dictionary are treated as a filename match pattern
+applied to that component of URLs, unless they start with a ^ in which
+case they are treated as a regular expression match.  If all the
+specified component matches for a given list item succeed, the URL is
+blacklisted.
+
+Example configuration:
+```yaml
+url_preview_url_blacklist:
+  # blacklist any URL with a username in its URI
+  - username: '*'
+
+  # blacklist all *.google.com URLs
+  - netloc: 'google.com'
+  - netloc: '*.google.com'
+
+  # blacklist all plain HTTP URLs
+  - scheme: 'http'
+
+  # blacklist http(s)://www.acme.com/foo
+  - netloc: 'www.acme.com'
+    path: '/foo'
+
+  # blacklist any URL with a literal IPv4 address
+  - netloc: '^[0-9]+\.[0-9]+\.[0-9]+\.[0-9]+$'
+```
+---
+Config option: `max_spider_size`
+
+The largest allowed URL preview spidering size in bytes. Defaults to 10M.
+
+Example configuration:
+```yaml
+max_spider_size: 8M
+```
+---
+Config option: `url_preview_language`
+
+A list of values for the Accept-Language HTTP header used when
+downloading webpages during URL preview generation. This allows
+Synapse to specify the preferred languages that URL previews should
+be in when communicating with remote servers.
+
+Each value is a IETF language tag; a 2-3 letter identifier for a
+language, optionally followed by subtags separated by '-', specifying
+a country or region variant.
+
+Multiple values can be provided, and a weight can be added to each by
+using quality value syntax (;q=). '*' translates to any language.
+
+Defaults to "en".
+
+Example configuration:
+```yaml
+ url_preview_accept_language:
+   - en-UK
+   - en-US;q=0.9
+   - fr;q=0.8
+   - *;q=0.7
+```
+----
+Config option: `oembed`
+
+oEmbed allows for easier embedding content from a website. It can be
+used for generating URLs previews of services which support it. A default list of oEmbed providers
+is included with Synapse. Set `disable_default_providers` to true to disable using
+these default oEmbed URLs. Use `additional_providers` to specify additional files with oEmbed configuration (each 
+should be in the form of providers.json). By default this list is empty. 
+
+Example configuration:
+```yaml
+oembed:
+  disable_default_providers: true
+  additional_providers:
+    - oembed/my_providers.json
+```
+---
+## Captcha ##
+
+See [here](../../CAPTCHA_SETUP.md) for full details on setting up captcha.
+
+---
+Config option: `recaptcha_public_key`
+
+This homeserver's ReCAPTCHA public key. Must be specified if `enable_registration_captcha` is 
+enabled.
+
+Example configuration:
+```yaml
+recaptcha_public_key: "YOUR_PUBLIC_KEY"
+```
+---
+Config option: `recaptcha_private_key` 
+
+This homeserver's ReCAPTCHA private key. Must be specified if `enable_registration_captcha` is 
+enabled.
+
+Example configuration:
+```yaml
+recaptcha_private_key: "YOUR_PRIVATE_KEY"
+```
+---
+Config option: `enable_registration_captcha`
+
+Set to true to enable ReCaptcha checks when registering, preventing signup
+unless a captcha is answered. Requires a valid ReCaptcha public/private key. 
+Defaults to false.
+
+Example configuration:
+```yaml
+enable_registration_captcha: true
+```
+---
+Config option: `recaptcha_siteverify_api`
+
+The API endpoint to use for verifying `m.login.recaptcha` responses.
+Defaults to `https://www.recaptcha.net/recaptcha/api/siteverify`.
+
+Example configuration:
+```yaml
+recaptcha_siteverify_api: "https://my.recaptcha.site"
+```
+---
+## TURN ##
+Options related to adding a TURN server to Synapse.
+
+---
+Config option: `turn_uris`
+
+The public URIs of the TURN server to give to clients.
+
+Example configuration:
+```yaml
+turn_uris: [turn:example.org]
+```
+---
+Config option: `turn_shared_secret`
+
+The shared secret used to compute passwords for the TURN server.
+
+Example configuration:
+```yaml
+turn_shared_secret: "YOUR_SHARED_SECRET"
+```
+----
+Config options: `turn_username` and `turn_password`
+
+The Username and password if the TURN server needs them and does not use a token.
+
+Example configuration:
+```yaml
+turn_username: "TURNSERVER_USERNAME"
+turn_password: "TURNSERVER_PASSWORD"
+```
+---
+Config option: `turn_user_lifetime`
+
+How long generated TURN credentials last. Defaults to 1h.
+
+Example configuration:
+```yaml
+turn_user_lifetime: 2h
+```
+---
+Config option: `turn_allow_guests`
+
+Whether guests should be allowed to use the TURN server. This defaults to true, otherwise
+VoIP will be unreliable for guests. However, it does introduce a slight security risk as
+it allows users to connect to arbitrary endpoints without having first signed up for a valid account (e.g. by passing a CAPTCHA).
+
+Example configuration:
+```yaml
+turn_allow_guests: false
+```
+---
+## Registration ##
+
+Registration can be rate-limited using the parameters in the [Ratelimiting](#ratelimiting) section of this manual.
+
+---
+Config option: `enable_registration`
+
+Enable registration for new users. Defaults to false. It is highly recommended that if you enable registration,
+you use either captcha, email, or token-based verification to verify that new users are not bots. In order to enable registration 
+without any verification, you must also set `enable_registration_without_verification` to true.
+
+Example configuration:
+```yaml
+enable_registration: true
+```
+---
+Config option: `enable_registration_without_verification`
+Enable registration without email or captcha verification. Note: this option is *not* recommended,
+as registration without verification is a known vector for spam and abuse. Defaults to false. Has no effect
+unless `enable_registration` is also enabled.
+
+Example configuration:
+```yaml
+enable_registration_without_verification: true
+```
+---
+Config option: `session_lifetime`
+
+Time that a user's session remains valid for, after they log in.
+
+Note that this is not currently compatible with guest logins.
+
+Note also that this is calculated at login time: changes are not applied retrospectively to users who have already 
+logged in.
+
+By default, this is infinite.
+
+Example configuration:
+```yaml
+session_lifetime: 24h
+```
+----
+Config option: `refresh_access_token_lifetime`
+
+Time that an access token remains valid for, if the session is using refresh tokens.
+
+For more information about refresh tokens, please see the [manual](user_authentication/refresh_tokens.md).
+
+Note that this only applies to clients which advertise support for refresh tokens.
+
+Note also that this is calculated at login time and refresh time: changes are not applied to 
+existing sessions until they are refreshed.
+
+By default, this is 5 minutes.
+
+Example configuration:
+```yaml
+refreshable_access_token_lifetime: 10m
+```
+---
+Config option: `refresh_token_lifetime: 24h`
+
+Time that a refresh token remains valid for (provided that it is not
+exchanged for another one first).
+This option can be used to automatically log-out inactive sessions.
+Please see the manual for more information.
+
+Note also that this is calculated at login time and refresh time:
+changes are not applied to existing sessions until they are refreshed.
+
+By default, this is infinite.
+
+Example configuration:
+```yaml
+refresh_token_lifetime: 24h
+```
+---
+Config option: `nonrefreshable_access_token_lifetime`
+
+Time that an access token remains valid for, if the session is NOT
+using refresh tokens.
+
+Please note that not all clients support refresh tokens, so setting
+this to a short value may be inconvenient for some users who will
+then be logged out frequently.
+
+Note also that this is calculated at login time: changes are not applied
+retrospectively to existing sessions for users that have already logged in.
+
+By default, this is infinite.
+
+Example configuration:
+```yaml
+nonrefreshable_access_token_lifetime: 24h
+```
+---
+Config option: `registrations_require_3pid`
+
+If this is set, the user must provide all of the specified types of 3PID when registering.
+
+Example configuration:
+```yaml
+registrations_require_3pid:
+  - email
+  - msisdn
+```
+---
+Config option: `disable_msisdn_registration`
+
+Explicitly disable asking for MSISDNs from the registration
+flow (overrides `registrations_require_3pid` if MSISDNs are set as required).
+
+Example configuration:
+```yaml
+disable_msisdn_registration: true
+```
+---
+Config option: `allowed_local_3pids`
+
+Mandate that users are only allowed to associate certain formats of
+3PIDs with accounts on this server, as specified by the `medium` and `pattern` sub-options.
+
+Example configuration:
+```yaml
+allowed_local_3pids:
+  - medium: email
+    pattern: '^[^@]+@matrix\.org$'
+  - medium: email
+    pattern: '^[^@]+@vector\.im$'
+  - medium: msisdn
+    pattern: '\+44'
+```
+---
+Config option: `enable_3pid_lookup`
+
+Enable 3PIDs lookup requests to identity servers from this server. Defaults to true.
+
+Example configuration:
+```yaml
+enable_3pid_lookup: false
+```
+---
+Config option: `registration_requires_token`
+
+Require users to submit a token during registration.
+Tokens can be managed using the admin [API](../administration/admin_api/registration_tokens.md).
+Note that `enable_registration` must be set to true.
+Disabling this option will not delete any tokens previously generated.
+Defaults to false. Set to true to enable.  
+
+Example configuration:
+```yaml
+registration_requires_token: true
+```
+---
+Config option: `registration_shared_secret`
+
+If set, allows registration of standard or admin accounts by anyone who
+has the shared secret, even if registration is otherwise disabled.
+
+Example configuration:
+```yaml
+registration_shared_secret: <PRIVATE STRING>
+```
+---
+Config option: `bcrypt_rounds`
+
+Set the number of bcrypt rounds used to generate password hash.
+Larger numbers increase the work factor needed to generate the hash.
+The default number is 12 (which equates to 2^12 rounds).
+N.B. that increasing this will exponentially increase the time required
+to register or login - e.g. 24 => 2^24 rounds which will take >20 mins.
+Example configuration:
+```yaml
+bcrypt_rounds: 14
+```
+---
+Config option: `allow_guest_access`
+
+Allows users to register as guests without a password/email/etc, and
+participate in rooms hosted on this server which have been made
+accessible to anonymous users. Defaults to false.
+
+Example configuration:
+```yaml
+allow_guest_access: true
+```
+---
+Config option: `default_identity_server`
+
+The identity server which we suggest that clients should use when users log
+in on this server.
+
+(By default, no suggestion is made, so it is left up to the client.
+This setting is ignored unless `public_baseurl` is also explicitly set.)
+
+Example configuration:
+```yaml
+default_identity_server: https://matrix.org
+```
+---
+Config option: `account_threepid_delegates`
+
+Handle threepid (email/phone etc) registration and password resets through a set of
+*trusted* identity servers. Note that this allows the configured identity server to
+reset passwords for accounts!
+
+Be aware that if `email` is not set, and SMTP options have not been
+configured in the email config block, registration and user password resets via
+email will be globally disabled.
+
+Additionally, if `msisdn` is not set, registration and password resets via msisdn
+will be disabled regardless, and users will not be able to associate an msisdn
+identifier to their account. This is due to Synapse currently not supporting
+any method of sending SMS messages on its own.
+
+To enable using an identity server for operations regarding a particular third-party
+identifier type, set the value to the URL of that identity server as shown in the
+examples below.
+
+Servers handling the these requests must answer the `/requestToken` endpoints defined
+by the Matrix Identity Service API [specification](https://matrix.org/docs/spec/identity_service/latest).
+
+Example configuration:
+```yaml
+account_threepid_delegates:
+    email: https://example.com     # Delegate email sending to example.com
+    msisdn: http://localhost:8090  # Delegate SMS sending to this local process
+```
+---
+Config option: `enable_set_displayname`
+
+Whether users are allowed to change their displayname after it has
+been initially set. Useful when provisioning users based on the
+contents of a third-party directory.
+
+Does not apply to server administrators. Defaults to true.
+
+Example configuration:
+```yaml
+enable_set_displayname: false
+```
+---
+Config option: `enable_set_avatar_url`
+
+Whether users are allowed to change their avatar after it has been
+initially set. Useful when provisioning users based on the contents
+of a third-party directory.
+
+Does not apply to server administrators. Defaults to true.
+
+Example configuration:
+```yaml
+enable_set_avatar_url: false
+```
+---
+Config option: `enable_3pid_changes`
+
+Whether users can change the third-party IDs associated with their accounts
+(email address and msisdn).
+
+Defaults to true.
+
+Example configuration:
+```yaml
+enable_3pid_changes: false
+```
+---
+Config option: `auto_join_rooms`
+
+Users who register on this homeserver will automatically be joined
+to the rooms listed under this option.
+
+By default, any room aliases included in this list will be created
+as a publicly joinable room when the first user registers for the
+homeserver. If the room already exists, make certain it is a publicly joinable
+room, i.e. the join rule of the room must be set to 'public'. You can find more options
+relating to auto-joining rooms below. 
+
+Example configuration:
+```yaml
+auto_join_rooms:
+  - "#exampleroom:example.com"
+  - "#anotherexampleroom:example.com"
+```
+---
+Config option: `autocreate_auto_join_rooms`
+
+Where `auto_join_rooms` are specified, setting this flag ensures that
+the rooms exist by creating them when the first user on the
+homeserver registers.
+
+By default the auto-created rooms are publicly joinable from any federated
+server. Use the `autocreate_auto_join_rooms_federated` and
+`autocreate_auto_join_room_preset` settings to customise this behaviour.
+
+Setting to false means that if the rooms are not manually created,
+users cannot be auto-joined since they do not exist.
+
+Defaults to true.
+
+Example configuration:
+```yaml
+autocreate_auto_join_rooms: false
+```
+---
+Config option: `autocreate_auto_join_rooms_federated`
+
+Whether the rooms listen in `auto_join_rooms` that are auto-created are available
+via federation. Only has an effect if `autocreate_auto_join_rooms` is true.
+
+Note that whether a room is federated cannot be modified after
+creation.
+
+Defaults to true: the room will be joinable from other servers.
+Set to false to prevent users from other homeservers from
+joining these rooms.
+
+Example configuration:
+```yaml
+autocreate_auto_join_rooms_federated: false
+```
+---
+Config option: `autocreate_auto_join_room_preset`
+
+The room preset to use when auto-creating one of `auto_join_rooms`. Only has an
+effect if `autocreate_auto_join_rooms` is true.
+
+Possible values for this option are:
+* "public_chat": the room is joinable by anyone, including
+  federated servers if `autocreate_auto_join_rooms_federated` is true (the default).
+* "private_chat": an invitation is required to join these rooms. 
+* "trusted_private_chat": an invitation is required to join this room and the invitee is
+  assigned a power level of 100 upon joining the room. 
+
+If a value of "private_chat" or "trusted_private_chat" is used then
+`auto_join_mxid_localpart` must also be configured.
+
+Defaults to "public_chat".
+
+Example configuration:
+```yaml
+autocreate_auto_join_room_preset: private_chat
+```
+---
+Config option: `auto_join_mxid_localpart`
+
+The local part of the user id which is used to create `auto_join_rooms` if
+`autocreate_auto_join_rooms` is true. If this is not provided then the
+initial user account that registers will be used to create the rooms.
+
+The user id is also used to invite new users to any auto-join rooms which
+are set to invite-only.
+
+It *must* be configured if `autocreate_auto_join_room_preset` is set to
+"private_chat" or "trusted_private_chat".
+
+Note that this must be specified in order for new users to be correctly
+invited to any auto-join rooms which have been set to invite-only (either
+at the time of creation or subsequently).
+
+Note that, if the room already exists, this user must be joined and
+have the appropriate permissions to invite new members.
+
+Example configuration:
+```yaml
+auto_join_mxid_localpart: system
+```
+---
+Config option: `auto_join_rooms_for_guests`
+ 
+When `auto_join_rooms` is specified, setting this flag to false prevents
+guest accounts from being automatically joined to the rooms.
+
+Defaults to true.
+
+Example configuration:
+```yaml
+auto_join_rooms_for_guests: false
+```
+---
+Config option: `inhibit_user_in_use_error`
+ 
+Whether to inhibit errors raised when registering a new account if the user ID
+already exists. If turned on, requests to `/register/available` will always
+show a user ID as available, and Synapse won't raise an error when starting
+a registration with a user ID that already exists. However, Synapse will still
+raise an error if the registration completes and the username conflicts.
+
+Defaults to false.
+
+Example configuration:
+```yaml
+inhibit_user_in_use_error: true
+```
+---
+## Metrics ###
+Config options related to metrics.
+
+---
+Config option: `enable_metrics`
+
+Set to true to enable collection and rendering of performance metrics. 
+Defaults to false.
+
+Example configuration:
+```yaml
+enable_metrics: true
+```
+---
+Config option: `sentry`
+
+Use this option to enable sentry integration. Provide the DSN assigned to you by sentry
+with the `dsn` setting. 
+
+NOTE: While attempts are made to ensure that the logs don't contain
+any sensitive information, this cannot be guaranteed. By enabling
+this option the sentry server may therefore receive sensitive 
+information, and it in turn may then disseminate sensitive information
+through insecure notification channels if so configured.
+
+Example configuration:
+```yaml
+sentry:
+    dsn: "..."
+```
+---
+Config option: `metrics_flags`
+
+Flags to enable Prometheus metrics which are not suitable to be
+enabled by default, either for performance reasons or limited use.
+Currently the only option is `known_servers`, which publishes 
+`synapse_federation_known_servers`, a gauge of the number of
+servers this homeserver knows about, including itself. May cause
+performance problems on large homeservers.
+
+Example configuration:
+```yaml
+metrics_flags:
+    known_servers: true
+```
+---
+Config option: `report_stats`
+
+Whether or not to report anonymized homeserver usage statistics. This is originally
+set when generating the config. Set this option to true or false to change the current
+behavior. 
+
+Example configuration:
+```yaml
+report_stats: true
+```
+---
+Config option: `report_stats_endpoint`
+
+The endpoint to report the anonymized homeserver usage statistics to.
+Defaults to https://matrix.org/report-usage-stats/push
+
+Example configuration:
+```yaml
+report_stats_endpoint: https://example.com/report-usage-stats/push
+```
+---
+## API Configuration ##
+Config settings related to the client/server API
+
+---
+Config option: `room_prejoin_state:`
+
+Controls for the state that is shared with users who receive an invite
+to a room. By default, the following state event types are shared with users who 
+receive invites to the room:
+- m.room.join_rules
+- m.room.canonical_alias
+- m.room.avatar
+- m.room.encryption
+- m.room.name
+- m.room.create
+- m.room.topic
+
+To change the default behavior, use the following sub-options:
+* `disable_default_event_types`: set to true to disable the above defaults. If this 
+   is enabled, only the event types listed in `additional_event_types` are shared.
+   Defaults to false.
+* `additional_event_types`: Additional state event types to share with users when they are invited
+   to a room. By default, this list is empty (so only the default event types are shared).
+
+Example configuration:
+```yaml
+room_prejoin_state:
+   disable_default_event_types: true
+   additional_event_types:
+     - org.example.custom.event.type
+     - m.room.join_rules
+```
+---
+Config option: `track_puppeted_user_ips`
+
+We record the IP address of clients used to access the API for various
+reasons, including displaying it to the user in the "Where you're signed in"
+dialog.
+
+By default, when puppeting another user via the admin API, the client IP
+address is recorded against the user who created the access token (ie, the
+admin user), and *not* the puppeted user.
+
+Set this option to true to also record the IP address against the puppeted
+user. (This also means that the puppeted user will count as an "active" user
+for the purpose of monthly active user tracking - see `limit_usage_by_mau` etc
+above.)
+
+Example configuration:
+```yaml
+track_puppeted_user_ips: true
+```
+---
+Config option: `app_service_config_files`
+
+A list of application service config files to use.
+
+Example configuration:
+```yaml
+app_service_config_files:
+  - app_service_1.yaml
+  - app_service_2.yaml
+```
+---
+Config option: `track_appservice_user_ips`
+
+Defaults to false. Set to true to enable tracking of application service IP addresses.
+Implicitly enables MAU tracking for application service users.
+
+Example configuration:
+```yaml
+track_appservice_user_ips: true
+```
+---
+Config option: `macaroon_secret_key`
+
+A secret which is used to sign access tokens. If none is specified,
+the `registration_shared_secret` is used, if one is given; otherwise,
+a secret key is derived from the signing key.
+
+Example configuration:
+```yaml
+macaroon_secret_key: <PRIVATE STRING>
+```
+---
+Config option: `form_secret`
+
+A secret which is used to calculate HMACs for form values, to stop
+falsification of values. Must be specified for the User Consent
+forms to work.
+
+Example configuration:
+```yaml
+form_secret: <PRIVATE STRING>
+```
+---
+## Signing Keys ##
+Config options relating to signing keys
+
+---
+Config option: `signing_key_path`
+
+Path to the signing key to sign messages with.
+
+Example configuration:
+```yaml
+signing_key_path: "CONFDIR/SERVERNAME.signing.key"
+```
+--- 
+Config option: `old_signing_keys`
+
+The keys that the server used to sign messages with but won't use
+to sign new messages. For each key, `key` should be the base64-encoded public key, and
+`expired_ts`should be the time (in milliseconds since the unix epoch) that
+it was last used.
+
+It is possible to build an entry from an old `signing.key` file using the
+`export_signing_key` script which is provided with synapse.
+
+Example configuration:
+```yaml
+old_signing_keys:
+  "ed25519:id": { key: "base64string", expired_ts: 123456789123 }
+```
+---
+Config option: `key_refresh_interval`
+
+How long key response published by this server is valid for.
+Used to set the `valid_until_ts` in `/key/v2` APIs.
+Determines how quickly servers will query to check which keys
+are still valid. Defaults to 1d.
+
+Example configuration:
+```yaml
+key_refresh_interval: 2d
+```
+---
+Config option: `trusted_key_servers:`
+
+The trusted servers to download signing keys from.
+
+When we need to fetch a signing key, each server is tried in parallel.
+
+Normally, the connection to the key server is validated via TLS certificates.
+Additional security can be provided by configuring a `verify key`, which
+will make synapse check that the response is signed by that key.
+
+This setting supercedes an older setting named `perspectives`. The old format
+is still supported for backwards-compatibility, but it is deprecated.
+
+`trusted_key_servers` defaults to matrix.org, but using it will generate a
+warning on start-up. To suppress this warning, set
+`suppress_key_server_warning` to true.
+
+Options for each entry in the list include:
+* `server_name`: the name of the server. Required.
+* `verify_keys`: an optional map from key id to base64-encoded public key.
+   If specified, we will check that the response is signed by at least
+   one of the given keys.
+* `accept_keys_insecurely`: a boolean. Normally, if `verify_keys` is unset,
+   and `federation_verify_certificates` is not `true`, synapse will refuse 
+   to start, because this would allow anyone who can spoof DNS responses
+   to masquerade as the trusted key server. If you know what you are doing
+   and are sure that your network environment provides a secure connection
+   to the key server, you can set this to `true` to override this behaviour.
+
+Example configuration #1:
+```yaml
+trusted_key_servers:
+  - server_name: "my_trusted_server.example.com"
+    verify_keys:
+      "ed25519:auto": "abcdefghijklmnopqrstuvwxyzabcdefghijklmopqr"
+  - server_name: "my_other_trusted_server.example.com"
+```
+Example configuration #2:
+```yaml
+trusted_key_servers:
+  - server_name: "matrix.org"
+```
+---
+Config option: `suppress_key_server_warning`
+
+Set the following to true to disable the warning that is emitted when the
+`trusted_key_servers` include 'matrix.org'. See above.
+
+Example configuration:
+```yaml
+suppress_key_server_warning: true
+```
+---
+Config option: `key_server_signing_keys_path`
+
+The signing keys to use when acting as a trusted key server. If not specified
+defaults to the server signing key.
+
+Can contain multiple keys, one per line.
+
+Example configuration:
+```yaml
+key_server_signing_keys_path: "key_server_signing_keys.key"
+```
+---
+## Single sign-on integration ##
+
+The following settings can be used to make Synapse use a single sign-on
+provider for authentication, instead of its internal password database.
+
+You will probably also want to set the following options to false to
+disable the regular login/registration flows:
+   * `enable_registration`
+   * `password_config.enabled`
+
+You will also want to investigate the settings under the "sso" configuration
+section below.
+
+---
+Config option: `saml2_config`
+
+Enable SAML2 for registration and login. Uses pysaml2. To learn more about pysaml and
+to find a full list options for configuring pysaml, read the docs [here](https://pysaml2.readthedocs.io/en/latest/).
+
+At least one of `sp_config` or `config_path` must be set in this section to
+enable SAML login. You can either put your entire pysaml config inline using the `sp_config`
+option, or you can specify a path to a psyaml config file with the sub-option `config_path`.
+This setting has the following sub-options:
+
+* `sp_config`: the configuration for the pysaml2 Service Provider. See pysaml2 docs for format of config.
+   Default values will be used for the `entityid` and `service` settings,
+   so it is not normally necessary to specify them unless you need to
+   override them. Here are a few useful sub-options for configuring pysaml:
+   * `metadata`: Point this to the IdP's metadata. You must provide either a local
+      file via the `local` attribute or (preferably) a URL via the
+      `remote` attribute.
+   * `accepted_time_diff: 3`: Allowed clock difference in seconds between the homeserver and IdP.
+      Defaults to 0.
+   * `service`: By default, the user has to go to our login page first. If you'd like
+     to allow IdP-initiated login, set `allow_unsolicited` to true under `sp` in the `service`
+     section.
+* `config_path`: specify a separate pysaml2 configuration file thusly: 
+  `config_path: "CONFDIR/sp_conf.py"`
+* `saml_session_lifetime`: The lifetime of a SAML session. This defines how long a user has to
+   complete the authentication process, if `allow_unsolicited` is unset. The default is 15 minutes.
+* `user_mapping_provider`: Using this option, an external module can be provided as a 
+   custom solution to mapping attributes returned from a saml provider onto a matrix user. The 
+   `user_mapping_provider` has the following attributes:
+  * `module`: The custom module's class. 
+  * `config`: Custom configuration values for the module. Use the values provided in the 
+     example if you are using the built-in user_mapping_provider, or provide your own
+     config values for a custom class if you are using one. This section will be passed as a Python
+     dictionary to the module's `parse_config` method. The built-in provider takes the following two
+     options:
+      * `mxid_source_attribute`: The SAML attribute (after mapping via the attribute maps) to use
+          to derive the Matrix ID from. It is 'uid' by default. Note: This used to be configured by the
+          `saml2_config.mxid_source_attribute option`. If that is still defined, its value will be used instead.
+      * `mxid_mapping`: The mapping system to use for mapping the saml attribute onto a
+         matrix ID. Options include: `hexencode` (which maps unpermitted characters to '=xx')
+         and `dotreplace` (which replaces unpermitted characters with '.').
+         The default is `hexencode`. Note: This used to be configured by the
+         `saml2_config.mxid_mapping option`. If that is still defined, its value will be used instead.
+* `grandfathered_mxid_source_attribute`: In previous versions of synapse, the mapping from SAML attribute to
+   MXID was always calculated dynamically rather than stored in a table. For backwards- compatibility, we will look for `user_ids`
+   matching such a pattern before creating a new account. This setting controls the SAML attribute which will be used for this
+   backwards-compatibility lookup. Typically it should be 'uid', but if the attribute maps are changed, it may be necessary to change it.
+   The default is 'uid'. 
+* `attribute_requirements`: It is possible to configure Synapse to only allow logins if SAML attributes
+    match particular values. The requirements can be listed under
+   `attribute_requirements` as shown in the example. All of the listed attributes must
+    match for the login to be permitted.
+* `idp_entityid`: If the metadata XML contains multiple IdP entities then the `idp_entityid`
+   option must be set to the entity to redirect users to.
+   Most deployments only have a single IdP entity and so should omit this option.
+  
+
+Once SAML support is enabled, a metadata file will be exposed at
+`https://<server>:<port>/_synapse/client/saml2/metadata.xml`, which you may be able to
+use to configure your SAML IdP with. Alternatively, you can manually configure
+the IdP to use an ACS location of
+`https://<server>:<port>/_synapse/client/saml2/authn_response`.
+
+Example configuration:
+```yaml
+saml2_config:
+  sp_config:
+    metadata:
+      local: ["saml2/idp.xml"]
+      remote:
+        - url: https://our_idp/metadata.xml
+    accepted_time_diff: 3
+
+    service:
+      sp:
+        allow_unsolicited: true
+
+    # The examples below are just used to generate our metadata xml, and you
+    # may well not need them, depending on your setup. Alternatively you
+    # may need a whole lot more detail - see the pysaml2 docs!
+    description: ["My awesome SP", "en"]
+    name: ["Test SP", "en"]
+
+    ui_info:
+      display_name:
+        - lang: en
+          text: "Display Name is the descriptive name of your service."
+      description:
+        - lang: en
+          text: "Description should be a short paragraph explaining the purpose of the service."
+      information_url:
+        - lang: en
+          text: "https://example.com/terms-of-service"
+      privacy_statement_url:
+        - lang: en
+          text: "https://example.com/privacy-policy"
+      keywords:
+        - lang: en
+          text: ["Matrix", "Element"]
+      logo:
+        - lang: en
+          text: "https://example.com/logo.svg"
+          width: "200"
+          height: "80"
+
+    organization:
+      name: Example com
+      display_name:
+        - ["Example co", "en"]
+      url: "http://example.com"
+
+    contact_person:
+      - given_name: Bob
+        sur_name: "the Sysadmin"
+        email_address": ["admin@example.com"]
+        contact_type": technical
+        
+  saml_session_lifetime: 5m
+  
+  user_mapping_provider:
+    # Below options are intended for the built-in provider, they should be 
+    # changed if using a custom module. 
+    config:
+      mxid_source_attribute: displayName
+      mxid_mapping: dotreplace
+  
+  grandfathered_mxid_source_attribute: upn
+
+  attribute_requirements:
+    - attribute: userGroup
+      value: "staff"
+    - attribute: department
+      value: "sales"
+
+  idp_entityid: 'https://our_idp/entityid'
+```
+---
+Config option: `oidc_providers`
+
+List of OpenID Connect (OIDC) / OAuth 2.0 identity providers, for registration
+and login. See [here](../../openid.md)
+for information on how to configure these options.
+
+For backwards compatibility, it is also possible to configure a single OIDC
+provider via an `oidc_config` setting. This is now deprecated and admins are
+advised to migrate to the `oidc_providers` format. (When doing that migration,
+use `oidc` for the `idp_id` to ensure that existing users continue to be
+recognised.)
+
+Options for each entry include:
+* `idp_id`: a unique identifier for this identity provider. Used internally
+   by Synapse; should be a single word such as 'github'.
+   Note that, if this is changed, users authenticating via that provider
+   will no longer be recognised as the same user!
+   (Use "oidc" here if you are migrating from an old `oidc_config` configuration.)
+
+* `idp_name`: A user-facing name for this identity provider, which is used to
+   offer the user a choice of login mechanisms.
+
+* `idp_icon`: An optional icon for this identity provider, which is presented
+   by clients and Synapse's own IdP picker page. If given, must be an
+   MXC URI of the format mxc://<server-name>/<media-id>. (An easy way to
+   obtain such an MXC URI is to upload an image to an (unencrypted) room
+   and then copy the "url" from the source of the event.)
+
+* `idp_brand`: An optional brand for this identity provider, allowing clients
+   to style the login flow according to the identity provider in question.
+   See the [spec](https://spec.matrix.org/latest/) for possible options here.
+
+* `discover`: set to false to disable the use of the OIDC discovery mechanism
+  to discover endpoints. Defaults to true.
+
+* `issuer`: Required. The OIDC issuer. Used to validate tokens and (if discovery
+   is enabled) to discover the provider's endpoints.
+
+* `client_id`: Required. oauth2 client id to use.
+
+* `client_secret`: oauth2 client secret to use. May be omitted if
+  `client_secret_jwt_key` is given, or if `client_auth_method` is 'none'.
+
+* `client_secret_jwt_key`: Alternative to client_secret: details of a key used
+   to create a JSON Web Token to be used as an OAuth2 client secret. If
+   given, must be a dictionary with the following properties:
+
+  * `key`: a pem-encoded signing key. Must be a suitable key for the
+    algorithm specified. Required unless `key_file` is given.
+
+  * `key_file`: the path to file containing a pem-encoded signing key file.
+     Required unless `key` is given.
+
+  * `jwt_header`: a dictionary giving properties to include in the JWT
+     header. Must include the key `alg`, giving the algorithm used to
+     sign the JWT, such as "ES256", using the JWA identifiers in
+     RFC7518.
+
+  * `jwt_payload`: an optional dictionary giving properties to include in
+    the JWT payload. Normally this should include an `iss` key.
+
+* `client_auth_method`: auth method to use when exchanging the token. Valid
+   values are `client_secret_basic` (default), `client_secret_post` and
+   `none`.
+
+* `scopes`: list of scopes to request. This should normally include the "openid"
+   scope. Defaults to ["openid"].
+
+* `authorization_endpoint`: the oauth2 authorization endpoint. Required if
+   provider discovery is disabled.
+
+* `token_endpoint`: the oauth2 token endpoint. Required if provider discovery is
+   disabled.
+
+* `userinfo_endpoint`: the OIDC userinfo endpoint. Required if discovery is
+   disabled and the 'openid' scope is not requested.
+
+* `jwks_uri`: URI where to fetch the JWKS. Required if discovery is disabled and
+   the 'openid' scope is used.
+
+* `skip_verification`: set to 'true' to skip metadata verification. Use this if
+   you are connecting to a provider that is not OpenID Connect compliant.
+   Defaults to false. Avoid this in production.
+
+* `user_profile_method`: Whether to fetch the user profile from the userinfo
+   endpoint, or to rely on the data returned in the id_token from the `token_endpoint`.
+   Valid values are: `auto` or `userinfo_endpoint`.
+   Defaults to `auto`, which uses the userinfo endpoint if `openid` is
+   not included in `scopes`. Set to `userinfo_endpoint` to always use the
+   userinfo endpoint.
+
+* `allow_existing_users`: set to true to allow a user logging in via OIDC to
+   match a pre-existing account instead of failing. This could be used if
+   switching from password logins to OIDC. Defaults to false.
+
+* `user_mapping_provider`: Configuration for how attributes returned from a OIDC
+   provider are mapped onto a matrix user. This setting has the following
+   sub-properties:
+
+     * `module`: The class name of a custom mapping module. Default is
+       `synapse.handlers.oidc.JinjaOidcMappingProvider`.
+        See https://matrix-org.github.io/synapse/latest/sso_mapping_providers.html#openid-mapping-providers
+        for information on implementing a custom mapping provider.
+
+     * `config`: Configuration for the mapping provider module. This section will
+        be passed as a Python dictionary to the user mapping provider
+        module's `parse_config` method.
+
+        For the default provider, the following settings are available:
+
+       * subject_claim: name of the claim containing a unique identifier
+         for the user. Defaults to 'sub', which OpenID Connect
+         compliant providers should provide.
+
+       * `localpart_template`: Jinja2 template for the localpart of the MXID.
+          If this is not set, the user will be prompted to choose their
+          own username (see the documentation for the `sso_auth_account_details.html` 
+          template). This template can use the `localpart_from_email` filter.
+
+       * `confirm_localpart`: Whether to prompt the user to validate (or
+          change) the generated localpart (see the documentation for the
+          'sso_auth_account_details.html' template), instead of
+          registering the account right away.
+
+       * `display_name_template`: Jinja2 template for the display name to set
+          on first login. If unset, no displayname will be set.
+
+       * `email_template`: Jinja2 template for the email address of the user.
+          If unset, no email address will be added to the account.
+                 
+       * `extra_attributes`: a map of Jinja2 templates for extra attributes
+          to send back to the client during login. Note that these are non-standard and clients will ignore them
+          without modifications.
+
+     When rendering, the Jinja2 templates are given a 'user' variable,
+     which is set to the claims returned by the UserInfo Endpoint and/or
+     in the ID Token.
+
+
+It is possible to configure Synapse to only allow logins if certain attributes 
+match particular values in the OIDC userinfo. The requirements can be listed under
+`attribute_requirements` as shown here:
+```yaml
+attribute_requirements:
+     - attribute: family_name
+       value: "Stephensson"
+     - attribute: groups
+       value: "admin"
+```
+All of the listed attributes must match for the login to be permitted. Additional attributes can be added to
+userinfo by expanding the `scopes` section of the OIDC config to retrieve
+additional information from the OIDC provider.
+
+If the OIDC claim is a list, then the attribute must match any value in the list.
+Otherwise, it must exactly match the value of the claim. Using the example 
+above, the `family_name` claim MUST be "Stephensson", but the `groups`
+claim MUST contain "admin".
+
+Example configuration:
+```yaml
+oidc_providers:
+  # Generic example
+  #
+  - idp_id: my_idp
+    idp_name: "My OpenID provider"
+    idp_icon: "mxc://example.com/mediaid"
+    discover: false
+    issuer: "https://accounts.example.com/"
+    client_id: "provided-by-your-issuer"
+    client_secret: "provided-by-your-issuer"
+    client_auth_method: client_secret_post
+    scopes: ["openid", "profile"]
+    authorization_endpoint: "https://accounts.example.com/oauth2/auth"
+    token_endpoint: "https://accounts.example.com/oauth2/token"
+    userinfo_endpoint: "https://accounts.example.com/userinfo"
+    jwks_uri: "https://accounts.example.com/.well-known/jwks.json"
+    skip_verification: true
+    user_mapping_provider:
+      config:
+        subject_claim: "id"
+        localpart_template: "{{ user.login }}"
+        display_name_template: "{{ user.name }}"
+        email_template: "{{ user.email }}"
+    attribute_requirements:
+      - attribute: userGroup
+        value: "synapseUsers"
+```
+---
+Config option: `cas_config`
+
+Enable Central Authentication Service (CAS) for registration and login.
+Has the following sub-options:
+* `enabled`: Set this to true to enable authorization against a CAS server.
+   Defaults to false.
+* `server_url`: The URL of the CAS authorization endpoint.
+* `displayname_attribute`: The attribute of the CAS response to use as the display name.
+   If no name is given here, no displayname will be set.
+* `required_attributes`:  It is possible to configure Synapse to only allow logins if CAS attributes
+   match particular values. All of the keys given below must exist
+   and the values must match the given value. Alternately if the given value
+   is `None` then any value is allowed (the attribute just must exist).
+   All of the listed attributes must match for the login to be permitted.
+
+Example configuration:
+```yaml
+cas_config:
+  enabled: true
+  server_url: "https://cas-server.com"
+  displayname_attribute: name
+  required_attributes:
+    userGroup: "staff"
+    department: None
+```
+---
+Config option: `sso`
+
+Additional settings to use with single-sign on systems such as OpenID Connect,
+SAML2 and CAS.
+
+Server admins can configure custom templates for pages related to SSO. See 
+[here](../../templates.md) for more information.
+
+Options include:
+* `client_whitelist`: A list of client URLs which are whitelisted so that the user does not
+   have to confirm giving access to their account to the URL. Any client
+   whose URL starts with an entry in the following list will not be subject
+   to an additional confirmation step after the SSO login is completed.
+   WARNING: An entry such as "https://my.client" is insecure, because it
+   will also match "https://my.client.evil.site", exposing your users to
+   phishing attacks from evil.site. To avoid this, include a slash after the
+   hostname: "https://my.client/".
+   The login fallback page (used by clients that don't natively support the
+   required login flows) is whitelisted in addition to any URLs in this list.
+   By default, this list contains only the login fallback page.
+* `update_profile_information`: Use this setting to keep a user's profile fields in sync with information from
+   the identity provider. Currently only syncing the displayname is supported. Fields 
+   are checked on every SSO login, and are updated if necessary.
+   Note that enabling this option will override user profile information,
+   regardless of whether users have opted-out of syncing that
+   information when first signing in. Defaults to false.
+
+
+Example configuration:
+```yaml
+sso:
+    client_whitelist:
+      - https://riot.im/develop
+      - https://my.custom.client/
+    update_profile_information: true
+```
+---
+Config option: `jwt_config`
+
+JSON web token integration. The following settings can be used to make
+Synapse JSON web tokens for authentication, instead of its internal
+password database.
+
+Each JSON Web Token needs to contain a "sub" (subject) claim, which is
+used as the localpart of the mxid.
+
+Additionally, the expiration time ("exp"), not before time ("nbf"),
+and issued at ("iat") claims are validated if present.
+
+Note that this is a non-standard login type and client support is
+expected to be non-existent.
+
+See [here](../../jwt.md) for more.
+
+Additional sub-options for this setting include:
+* `enabled`: Set to true to enable authorization using JSON web
+   tokens. Defaults to false.
+* `secret`: This is either the private shared secret or the public key used to
+   decode the contents of the JSON web token. Required if `enabled` is set to true.
+* `algorithm`: The algorithm used to sign the JSON web token. Supported algorithms are listed at
+   https://pyjwt.readthedocs.io/en/latest/algorithms.html Required if `enabled` is set to true.
+* `subject_claim`: Name of the claim containing a unique identifier for the user.
+   Optional, defaults to `sub`.
+* `issuer`: The issuer to validate the "iss" claim against. Optional. If provided the 
+   "iss" claim will be required and validated for all JSON web tokens.
+* `audiences`: A list of audiences to validate the "aud" claim against. Optional.
+   If provided the "aud" claim will be required and validated for all JSON web tokens.
+   Note that if the "aud" claim is included in a JSON web token then
+   validation will fail without configuring audiences.
+
+Example configuration:
+```yaml
+jwt_config:
+    enabled: true 
+    secret: "provided-by-your-issuer"
+    algorithm: "provided-by-your-issuer"
+    subject_claim: "name_of_claim"
+    issuer: "provided-by-your-issuer"
+    audiences:
+        - "provided-by-your-issuer"
+```
+---
+Config option: `password_config`
+
+Use this setting to enable password-based logins. 
+
+This setting has the following sub-options:
+* `enabled`: Defaults to true.
+* `localdb_enabled`: Set to false to disable authentication against the local password
+   database. This is ignored if `enabled` is false, and is only useful
+   if you have other `password_providers`. Defaults to true. 
+* `pepper`: Set the value here to a secret random string for extra security. # Uncomment and change to a secret random string for extra security.
+   DO NOT CHANGE THIS AFTER INITIAL SETUP!
+* `policy`: Define and enforce a password policy, such as minimum lengths for passwords, etc. 
+   Each parameter is optional. This is an implementation of MSC2000. Parameters are as follows:
+   * `enabled`: Defaults to false. Set to true to enable.
+   * `minimum_length`: Minimum accepted length for a password. Defaults to 0.
+   * `require_digit`: Whether a password must contain at least one digit.
+      Defaults to false.
+   * `require_symbol`: Whether a password must contain at least one symbol.
+      A symbol is any character that's not a number or a letter. Defaults to false.
+   * `require_lowercase`: Whether a password must contain at least one lowercase letter.
+      Defaults to false.
+   * `require_uppercase`: Whether a password must contain at least one uppercase letter.
+      Defaults to false.
+      
+
+Example configuration:
+```yaml
+password_config:
+   enabled: false
+   localdb_enabled: false
+   pepper: "EVEN_MORE_SECRET"
+
+   policy:
+      enabled: true
+      minimum_length: 15
+      require_digit: true
+      require_symbol: true
+      require_lowercase: true
+      require_uppercase: true
+```
+---
+Config option: `ui_auth`
+
+The amount of time to allow a user-interactive authentication session to be active.
+
+This defaults to 0, meaning the user is queried for their credentials 
+before every action, but this can be overridden to allow a single
+validation to be re-used.  This weakens the protections afforded by
+the user-interactive authentication process, by allowing for multiple
+(and potentially different) operations to use the same validation session.
+
+This is ignored for potentially "dangerous" operations (including
+deactivating an account, modifying an account password, and
+adding a 3PID).
+
+Use the `session_timeout` sub-option here to change the time allowed for credential validation.
+
+Example configuration:
+```yaml
+ui_auth:
+    session_timeout: "15s"
+```
+---
+Config option: `email`
+
+Configuration for sending emails from Synapse.
+
+Server admins can configure custom templates for email content. See
+[here](../../templates.md) for more information.
+
+This setting has the following sub-options:
+* `smtp_host`: The hostname of the outgoing SMTP server to use. Defaults to 'localhost'.
+* `smtp_port`: The port on the mail server for outgoing SMTP. Defaults to 25.
+* `smtp_user` and `smtp_pass`: Username/password for authentication to the SMTP server. By default, no
+   authentication is attempted.
+* `require_transport_security`: Set to true to require TLS transport security for SMTP.
+   By default, Synapse will connect over plain text, and will then switch to
+   TLS via STARTTLS *if the SMTP server supports it*. If this option is set,
+   Synapse will refuse to connect unless the server supports STARTTLS.
+* `enable_tls`: By default, if the server supports TLS, it will be used, and the server
+   must present a certificate that is valid for 'smtp_host'. If this option
+   is set to false, TLS will not be used.
+* `notif_from`: defines the "From" address to use when sending emails.
+    It must be set if email sending is enabled. The placeholder '%(app)s' will be replaced by the application name,
+    which is normally set in `app_name`, but may be overridden by the
+    Matrix client application. Note that the placeholder must be written '%(app)s', including the
+    trailing 's'.
+* `app_name`: `app_name` defines the default value for '%(app)s' in `notif_from` and email
+   subjects. It defaults to 'Matrix'.
+* `enable_notifs`: Set to true to enable sending emails for messages that the user
+   has missed. Disabled by default.
+* `notif_for_new_users`: Set to false to disable automatic subscription to email
+   notifications for new users. Enabled by default.
+* `client_base_url`: Custom URL for client links within the email notifications. By default
+   links will be based on "https://matrix.to". (This setting used to be called `riot_base_url`;
+   the old name is still supported for backwards-compatibility but is now deprecated.)
+* `validation_token_lifetime`: Configures the time that a validation email will expire after sending.
+   Defaults to 1h.
+* `invite_client_location`: The web client location to direct users to during an invite. This is passed
+   to the identity server as the `org.matrix.web_client_location` key. Defaults
+   to unset, giving no guidance to the identity server.
+* `subjects`: Subjects to use when sending emails from Synapse. The placeholder '%(app)s' will
+   be replaced with the value of the `app_name` setting, or by a value dictated by the Matrix client application.
+   In addition, each subject can use the following placeholders: '%(person)s', which will be replaced by the displayname
+   of the user(s) that sent the message(s), e.g. "Alice and Bob", and '%(room)s', which will be replaced by the name of the room the
+   message(s) have been sent to, e.g. "My super room". In addition, emails related to account administration will
+   can use the '%(server_name)s' placeholder, which will be replaced by the value of the
+   `server_name` setting in your Synapse configuration.
+   
+   Here is a list of subjects for notification emails that can be set: 
+     * `message_from_person_in_room`: Subject to use to notify about one message from one or more user(s) in a
+        room which has a name. Defaults to "[%(app)s] You have a message on %(app)s from %(person)s in the %(room)s room..."
+     * `message_from_person`: Subject to use to notify about one message from one or more user(s) in a
+        room which doesn't have a name. Defaults to "[%(app)s] You have a message on %(app)s from %(person)s..."
+     * `messages_from_person`: Subject to use to notify about multiple messages from one or more users in
+        a room which doesn't have a name. Defaults to "[%(app)s] You have messages on %(app)s from %(person)s..."
+     * `messages_in_room`: Subject to use to notify about multiple messages in a room which has a
+        name. Defaults to "[%(app)s] You have messages on %(app)s in the %(room)s room..."
+     * `messages_in_room_and_others`: Subject to use to notify about multiple messages in multiple rooms. 
+        Defaults to "[%(app)s] You have messages on %(app)s in the %(room)s room and others..."
+     * `messages_from_person_and_others`: Subject to use to notify about multiple messages from multiple persons in
+        multiple rooms. This is similar to the setting above except it's used when
+        the room in which the notification was triggered has no name. Defaults to 
+        "[%(app)s] You have messages on %(app)s from %(person)s and others..."
+     * `invite_from_person_to_room`: Subject to use to notify about an invite to a room which has a name. 
+        Defaults to  "[%(app)s] %(person)s has invited you to join the %(room)s room on %(app)s..."
+     * `invite_from_person`: Subject to use to notify about an invite to a room which doesn't have a
+        name. Defaults to "[%(app)s] %(person)s has invited you to chat on %(app)s..."
+     * `password_reset`: Subject to use when sending a password reset email. Defaults to "[%(server_name)s] Password reset"
+     * `email_validation`: Subject to use when sending a verification email to assert an address's
+        ownership. Defaults to "[%(server_name)s] Validate your email"
+
+Example configuration:
+```yaml
+email:
+  smtp_host: mail.server
+  smtp_port: 587
+  smtp_user: "exampleusername"
+  smtp_pass: "examplepassword"
+  require_transport_security: true
+  enable_tls: false
+  notif_from: "Your Friendly %(app)s homeserver <noreply@example.com>"
+  app_name: my_branded_matrix_server
+  enable_notifs: true
+  notif_for_new_users: false
+  client_base_url: "http://localhost/riot"
+  validation_token_lifetime: 15m
+  invite_client_location: https://app.element.io
+
+  subjects:
+    message_from_person_in_room: "[%(app)s] You have a message on %(app)s from %(person)s in the %(room)s room..."
+    message_from_person: "[%(app)s] You have a message on %(app)s from %(person)s..."
+    messages_from_person: "[%(app)s] You have messages on %(app)s from %(person)s..."
+    messages_in_room: "[%(app)s] You have messages on %(app)s in the %(room)s room..."
+    messages_in_room_and_others: "[%(app)s] You have messages on %(app)s in the %(room)s room and others..."
+    messages_from_person_and_others: "[%(app)s] You have messages on %(app)s from %(person)s and others..."
+    invite_from_person_to_room: "[%(app)s] %(person)s has invited you to join the %(room)s room on %(app)s..."
+    invite_from_person: "[%(app)s] %(person)s has invited you to chat on %(app)s..."
+    password_reset: "[%(server_name)s] Password reset"
+    email_validation: "[%(server_name)s] Validate your email"
+```
+---
+## Push ##
+Configuration settings related to push notifications
+
+---
+Config option: `push`
+
+This setting defines options for push notifications. 
+
+This option has a number of sub-options. They are as follows:
+* `include_content`: Clients requesting push notifications can either have the body of
+   the message sent in the notification poke along with other details
+   like the sender, or just the event ID and room ID (`event_id_only`).
+   If clients choose the to have the body sent, this option controls whether the
+   notification request includes the content of the event (other details
+   like the sender are still included). If `event_id_only` is enabled, it
+   has no effect.
+   For modern android devices the notification content will still appear
+   because it is loaded by the app. iPhone, however will send a
+   notification saying only that a message arrived and who it came from.
+   Defaults to true. Set to false to only include the event ID and room ID in push notification payloads.
+* `group_unread_count_by_room: false`: When a push notification is received, an unread count is also sent.
+   This number can either be calculated as the number of unread messages  for the user, or the number of *rooms* the 
+   user has unread messages in. Defaults to true, meaning push clients will see the number of
+   rooms with unread messages in them. Set to false to instead send the number
+   of unread messages.
+
+Example configuration:
+```yaml
+push:
+  include_content: false
+  group_unread_count_by_room: false
+```
+---
+## Rooms ##
+Config options relating to rooms.
+
+---
+Config option: `encryption_enabled_by_default`
+
+Controls whether locally-created rooms should be end-to-end encrypted by
+default.
+
+Possible options are "all", "invite", and "off". They are defined as:
+
+* "all": any locally-created room
+* "invite": any room created with the `private_chat` or `trusted_private_chat`
+   room creation presets
+* "off": this option will take no effect
+
+The default value is "off".
+
+Note that this option will only affect rooms created after it is set. It
+will also not affect rooms created by other servers.
+
+Example configuration:
+```yaml
+encryption_enabled_by_default_for_room_type: invite
+```
+---
+Config option: `enable_group_creation`
+
+Set to true to allow non-server-admin users to create groups on this server
+
+Example configuration:
+```yaml
+enable_group_creation: true
+```
+---
+Config option: `group_creation_prefix`
+
+If enabled/present, non-server admins can only create groups with local parts
+starting with this prefix.
+
+Example configuration:
+```yaml
+group_creation_prefix: "unofficial_"
+```
+---
+Config option: `user_directory`
+
+This setting defines options related to the user directory. 
+
+This option has the following sub-options:
+* `enabled`:  Defines whether users can search the user directory. If false then
+   empty responses are returned to all queries. Defaults to true.
+* `search_all_users`: Defines whether to search all users visible to your HS when searching
+   the user directory. If false, search results will only contain users
+    visible in public rooms and users sharing a room with the requester.
+    Defaults to false.
+    NB. If you set this to true, and the last time the user_directory search
+    indexes were (re)built was before Synapse 1.44, you'll have to
+    rebuild the indexes in order to search through all known users.
+    These indexes are built the first time Synapse starts; admins can
+    manually trigger a rebuild via API following the instructions at
+         https://matrix-org.github.io/synapse/latest/usage/administration/admin_api/background_updates.html#run
+    Set to true to return search results containing all known users, even if that
+    user does not share a room with the requester.
+* `prefer_local_users`: Defines whether to prefer local users in search query results.
+   If set to true, local users are more likely to appear above remote users when searching the 
+   user directory. Defaults to false.
+
+Example configuration:
+```yaml
+user_directory:
+    enabled: false
+    search_all_users: true
+    prefer_local_users: true
+```
+---
+Config option: `user_consent`
+
+For detailed instructions on user consent configuration, see [here](../../consent_tracking.md).
+
+Parts of this section are required if enabling the `consent` resource under
+`listeners`, in particular `template_dir` and `version`. # TODO: link `listeners`
+
+* `template_dir`: gives the location of the templates for the HTML forms.
+  This directory should contain one subdirectory per language (eg, `en`, `fr`),
+  and each language directory should contain the policy document (named as
+  <version>.html) and a success page (success.html).
+
+* `version`: specifies the 'current' version of the policy document. It defines
+   the version to be served by the consent resource if there is no 'v'
+   parameter.
+
+* `server_notice_content`: if enabled, will send a user a "Server Notice"
+   asking them to consent to the privacy policy. The `server_notices` section ##TODO: link
+   must also be configured for this to work. Notices will *not* be sent to
+   guest users unless `send_server_notice_to_guests` is set to true.
+
+* `block_events_error`, if set, will block any attempts to send events
+   until the user consents to the privacy policy. The value of the setting is
+   used as the text of the error.
+
+* `require_at_registration`, if enabled, will add a step to the registration
+   process, similar to how captcha works. Users will be required to accept the
+   policy before their account is created.
+
+* `policy_name` is the display name of the policy users will see when registering
+   for an account. Has no effect unless `require_at_registration` is enabled.
+   Defaults to "Privacy Policy".
+
+Example configuration:
+```yaml
+user_consent:
+  template_dir: res/templates/privacy
+  version: 1.0
+  server_notice_content:
+    msgtype: m.text
+    body: >-
+      To continue using this homeserver you must review and agree to the
+      terms and conditions at %(consent_uri)s
+  send_server_notice_to_guests: true
+  block_events_error: >-
+    To continue using this homeserver you must review and agree to the
+    terms and conditions at %(consent_uri)s
+  require_at_registration: false
+  policy_name: Privacy Policy
+```
+---
+Config option: `stats`
+
+Settings for local room and user statistics collection. See [here](../../room_and_user_statistics.md)
+for more. 
+
+* `enabled`: Set to false to disable room and user statistics. Note that doing
+   so may cause certain features (such as the room directory) not to work
+   correctly. Defaults to true. 
+
+Example configuration:
+```yaml
+stats:  
+  enabled: false
+```
+---
+Config option: `server_notices`
+
+Use this setting to enable a room which can be used to send notices
+from the server to users. It is a special room which users cannot leave; notices
+in the room come from a special "notices" user id.
+
+If you use this setting, you *must* define the `system_mxid_localpart`
+sub-setting, which defines the id of the user which will be used to send the
+notices.
+
+Sub-options for this setting include:
+* `system_mxid_display_name`: set the display name of the "notices" user
+* `system_mxid_avatar_url`: set the avatar for the "notices" user
+* `room_name`: set the room name of the server notices room
+
+Example configuration:
+```yaml
+server_notices:
+  system_mxid_localpart: notices
+  system_mxid_display_name: "Server Notices"
+  system_mxid_avatar_url: "mxc://server.com/oumMVlgDnLYFaPVkExemNVVZ"
+  room_name: "Server Notices"
+```
+---
+Config option: `enable_room_list_search`
+
+Set to false to disable searching the public room list. When disabled
+blocks searching local and remote room lists for local and remote
+users by always returning an empty list for all queries. Defaults to true. 
+
+Example configuration:
+```yaml
+enable_room_list_search: false
+```
+---
+Config option: `alias_creation`
+
+The `alias_creation` option controls who is allowed to create aliases
+on this server.
+
+The format of this option is a list of rules that contain globs that
+match against user_id, room_id and the new alias (fully qualified with
+server name). The action in the first rule that matches is taken,
+which can currently either be "allow" or "deny".
+
+Missing user_id/room_id/alias fields default to "*".
+
+If no rules match the request is denied. An empty list means no one
+can create aliases.
+
+Options for the rules include:
+* `user_id`: Matches against the creator of the alias. Defaults to "*".
+* `alias`: Matches against the alias being created. Defaults to "*".
+* `room_id`: Matches against the room ID the alias is being pointed at. Defaults to "*"
+* `action`: Whether to "allow" or "deny" the request if the rule matches. Defaults to allow. 
+
+Example configuration:
+```yaml
+alias_creation_rules:
+  - user_id: "bad_user"
+    alias: "spammy_alias"
+    room_id: "*"
+    action: deny
+```
+---
+Config options: `room_list_publication_rules`
+
+The `room_list_publication_rules` option controls who can publish and
+which rooms can be published in the public room list.
+
+The format of this option is the same as that for
+`alias_creation_rules`.
+
+If the room has one or more aliases associated with it, only one of
+the aliases needs to match the alias rule. If there are no aliases
+then only rules with `alias: *` match.
+
+If no rules match the request is denied. An empty list means no one
+can publish rooms.
+
+Options for the rules include:
+* `user_id`: Matches against the creator of the alias. Defaults to "*".
+* `alias`: Matches against any current local or canonical aliases associated with the room. Defaults to "*".
+* `room_id`: Matches against the room ID being published. Defaults to "*".
+* `action`: Whether to "allow" or "deny" the request if the rule matches. Defaults to allow. 
+
+Example configuration:
+```yaml
+room_list_publication_rules:
+  - user_id: "*"
+    alias: "*"
+    room_id: "*"
+    action: allow
+```
+---
+## Opentracing ##
+Configuration options related to Opentracing support.
+
+---
+Config option: `opentracing`
+
+These settings enable and configure opentracing, which implements distributed tracing.
+This allows you to observe the causal chains of events across servers
+including requests, key lookups etc., across any server running
+synapse or any other services which support opentracing
+(specifically those implemented with Jaeger).
+
+Sub-options include:
+* `enabled`: whether tracing is enabled. Set to true to enable. Disabled by default.
+* `homeserver_whitelist`: The list of homeservers we wish to send and receive span contexts and span baggage.
+   See [here](../../opentracing.md) for more. 
+   This is a list of regexes which are matched against the `server_name` of the homeserver.
+   By default, it is empty, so no servers are matched.
+* `force_tracing_for_users`: # A list of the matrix IDs of users whose requests will always be traced,
+   even if the tracing system would otherwise drop the traces due to probabilistic sampling.
+    By default, the list is empty.
+* `jaeger_config`: Jaeger can be configured to sample traces at different rates.
+   All configuration options provided by Jaeger can be set here. Jaeger's configuration is 
+   mostly related to trace sampling which is documented [here](https://www.jaegertracing.io/docs/latest/sampling/).
+
+Example configuration:
+```yaml
+opentracing:
+    enabled: true
+    homeserver_whitelist:
+      - ".*"
+    force_tracing_for_users:
+      - "@user1:server_name"
+      - "@user2:server_name"
+
+    jaeger_config:
+      sampler:
+        type: const
+        param: 1
+      logging:
+        false
+```
+---
+## Workers ##
+Configuration options related to workers.
+
+---
+Config option: `send_federation`
+
+Controls sending of outbound federation transactions on the main process.
+Set to false if using a federation sender worker. Defaults to true. 
+
+Example configuration:
+```yaml
+send_federation: false
+```
+---
+Config option: `federation_sender_instances`
+
+It is possible to run multiple federation sender workers, in which case the
+work is balanced across them. Use this setting to list the senders. 
+
+This configuration setting must be shared between all federation sender workers, and if
+changed all federation sender workers must be stopped at the same time and then
+started, to ensure that all instances are running with the same config (otherwise
+events may be dropped). 
+
+Example configuration:
+```yaml
+federation_sender_instances:
+  - federation_sender1
+```
+---
+Config option: `instance_map`
+
+When using workers this should be a map from worker name to the
+HTTP replication listener of the worker, if configured. 
+
+Example configuration:
+```yaml
+instance_map:
+  worker1:
+    host: localhost
+    port: 8034
+```
+---
+Config option: `stream_writers`
+
+Experimental: When using workers you can define which workers should
+handle event persistence and typing notifications. Any worker
+specified here must also be in the `instance_map`.
+
+Example configuration:
+```yaml
+stream_writers:
+  events: worker1
+  typing: worker1
+```
+---
+Config option: `run_background_task_on`
+
+The worker that is used to run background tasks (e.g. cleaning up expired
+data). If not provided this defaults to the main process.
+
+Example configuration:
+```yaml
+run_background_tasks_on: worker1
+```
+---
+Config option: `worker_replication_secret`
+
+A shared secret used by the replication APIs to authenticate HTTP requests
+from workers.
+
+By default this is unused and traffic is not authenticated.
+
+Example configuration:
+```yaml
+worker_replication_secret: "secret_secret"
+```
+Config option: `redis`
+
+Configuration for Redis when using workers. This *must* be enabled when
+using workers (unless using old style direct TCP configuration).
+This setting has the following sub-options:
+* `enabled`: whether to use Redis support. Defaults to false. 
+* `host` and `port`: Optional host and port to use to connect to redis. Defaults to
+   localhost and 6379
+* `password`: Optional password if configured on the Redis instance.
+
+Example configuration:
+```yaml
+redis:
+  enabled: true
+  host: localhost
+  port: 6379
+  password: <secret_password>
+```
+## Background Updates ##
+Configuration settings related to background updates. 
+
+---
+Config option: `background_updates`
+
+Background updates are database updates that are run in the background in batches.
+The duration, minimum batch size, default batch size, whether to sleep between batches and if so, how long to
+sleep can all be configured. This is helpful to speed up or slow down the updates.
+This setting has the following sub-options:
+* `background_update_duration_ms`: How long in milliseconds to run a batch of background updates for. Defaults to 100. 
+   Set a different time to change the default.
+* `sleep_enabled`: Whether to sleep between updates. Defaults to true. Set to false to change the default.
+* `sleep_duration_ms`: If sleeping between updates, how long in milliseconds to sleep for. Defaults to 1000.
+   Set a duration to change the default.
+* `min_batch_size`: Minimum size a batch of background updates can be. Must be greater than 0. Defaults to 1.
+   Set a size to change the default.
+* `default_batch_size`: The batch size to use for the first iteration of a new background update. The default is 100.
+   Set a size to change the default.
+
+Example configuration: 
+```yaml
+background_updates:
+    background_update_duration_ms: 500
+    sleep_enabled: false
+    sleep_duration_ms: 300
+    min_batch_size: 10
+    default_batch_size: 50
+```
\ No newline at end of file