Centralise the custom template directory (#10596)

Several configuration sections are using separate settings for custom template directories, which can be confusing. This PR adds a new top-level configuration for a custom template directory which is then used for every module. The only exception is the consent templates, since the consent template directory require a specific hierarchy, so it's probably better that it stays separate from everything else.

4 files changed, 270 insertions, 206 deletions

diff --git a/docs/SUMMARY.md b/docs/SUMMARY.md
index 3d320a1c43..56e0141c2b 100644
--- a/docs/SUMMARY.md
+++ b/docs/SUMMARY.md
@@ -21,6 +21,7 @@
     - [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)
+    - [Templates](templates.md)
     - [User Authentication](usage/configuration/user_authentication/README.md)
       - [Single-Sign On]()
         - [OpenID Connect](openid.md)
diff --git a/docs/sample_config.yaml b/docs/sample_config.yaml
index aeebcaf45f..3ec76d5abf 100644
--- a/docs/sample_config.yaml
+++ b/docs/sample_config.yaml
@@ -565,6 +565,19 @@ retention:
 #
 #next_link_domain_whitelist: ["matrix.org"]
 
+# Templates to use when generating email or HTML page contents.
+#
+templates:
+  # Directory in which Synapse will try to find template files 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 https://matrix-org.github.io/synapse/latest/templates.html for more
+  # information about using custom templates.
+  #
+  #custom_template_directory: /path/to/custom/templates/
+
 
 ## TLS ##
 
@@ -1895,6 +1908,9 @@ cas_config:
 # 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
+# https://matrix-org.github.io/synapse/latest/templates.html for more information.
+#
 sso:
     # 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
@@ -1927,169 +1943,6 @@ sso:
     #
     #update_profile_information: true
 
-    # Directory in which Synapse will try to find the template files below.
-    # If not set, or the files named below are not found within the template
-    # directory, default templates from within the Synapse package will be used.
-    #
-    # Synapse will look for the following templates in this directory:
-    #
-    # * HTML page to prompt the user to choose an Identity Provider during
-    #   login: 'sso_login_idp_picker.html'.
-    #
-    #   This is only used if multiple SSO Identity Providers are configured.
-    #
-    #   When rendering, this template is given the following variables:
-    #     * redirect_url: the URL that the user will be redirected to after
-    #       login.
-    #
-    #     * server_name: the homeserver's name.
-    #
-    #     * providers: a list of available Identity Providers. Each element is
-    #       an object with the following attributes:
-    #
-    #         * idp_id: unique identifier for the IdP
-    #         * idp_name: user-facing name for the IdP
-    #         * idp_icon: if specified in the IdP config, an MXC URI for an icon
-    #              for the IdP
-    #         * idp_brand: if specified in the IdP config, a textual identifier
-    #              for the brand of the IdP
-    #
-    #   The rendered HTML page should contain a form which submits its results
-    #   back as a GET request, with the following query parameters:
-    #
-    #     * redirectUrl: the client redirect URI (ie, the `redirect_url` passed
-    #       to the template)
-    #
-    #     * idp: the 'idp_id' of the chosen IDP.
-    #
-    # * HTML page to prompt new users to enter a userid and confirm other
-    #   details: 'sso_auth_account_details.html'. This is only shown if the
-    #   SSO implementation (with any user_mapping_provider) does not return
-    #   a localpart.
-    #
-    #   When rendering, this template is given the following variables:
-    #
-    #     * server_name: the homeserver's name.
-    #
-    #     * idp: details of the SSO Identity Provider that the user logged in
-    #       with: an object with the following attributes:
-    #
-    #         * idp_id: unique identifier for the IdP
-    #         * idp_name: user-facing name for the IdP
-    #         * idp_icon: if specified in the IdP config, an MXC URI for an icon
-    #              for the IdP
-    #         * idp_brand: if specified in the IdP config, a textual identifier
-    #              for the brand of the IdP
-    #
-    #     * user_attributes: an object containing details about the user that
-    #       we received from the IdP. May have the following attributes:
-    #
-    #         * display_name: the user's display_name
-    #         * emails: a list of email addresses
-    #
-    #   The template should render a form which submits the following fields:
-    #
-    #     * username: the localpart of the user's chosen user id
-    #
-    # * HTML page allowing the user to consent to the server's terms and
-    #   conditions. This is only shown for new users, and only if
-    #   `user_consent.require_at_registration` is set.
-    #
-    #   When rendering, this template is given the following variables:
-    #
-    #     * server_name: the homeserver's name.
-    #
-    #     * user_id: the user's matrix proposed ID.
-    #
-    #     * user_profile.display_name: the user's proposed display name, if any.
-    #
-    #     * consent_version: the version of the terms that the user will be
-    #       shown
-    #
-    #     * terms_url: a link to the page showing the terms.
-    #
-    #   The template should render a form which submits the following fields:
-    #
-    #     * accepted_version: the version of the terms accepted by the user
-    #       (ie, 'consent_version' from the input variables).
-    #
-    # * HTML page for a confirmation step before redirecting back to the client
-    #   with the login token: 'sso_redirect_confirm.html'.
-    #
-    #   When rendering, this template is given the following variables:
-    #
-    #     * redirect_url: the URL the user is about to be redirected to.
-    #
-    #     * display_url: the same as `redirect_url`, but with the query
-    #                    parameters stripped. The intention is to have a
-    #                    human-readable URL to show to users, not to use it as
-    #                    the final address to redirect to.
-    #
-    #     * server_name: the homeserver's name.
-    #
-    #     * new_user: a boolean indicating whether this is the user's first time
-    #          logging in.
-    #
-    #     * user_id: the user's matrix ID.
-    #
-    #     * user_profile.avatar_url: an MXC URI for the user's avatar, if any.
-    #           None if the user has not set an avatar.
-    #
-    #     * user_profile.display_name: the user's display name. None if the user
-    #           has not set a display name.
-    #
-    # * HTML page which notifies the user that they are authenticating to confirm
-    #   an operation on their account during the user interactive authentication
-    #   process: 'sso_auth_confirm.html'.
-    #
-    #   When rendering, this template is given the following variables:
-    #     * redirect_url: the URL the user is about to be redirected to.
-    #
-    #     * description: the operation which the user is being asked to confirm
-    #
-    #     * idp: details of the Identity Provider that we will use to confirm
-    #       the user's identity: an object with the following attributes:
-    #
-    #         * idp_id: unique identifier for the IdP
-    #         * idp_name: user-facing name for the IdP
-    #         * idp_icon: if specified in the IdP config, an MXC URI for an icon
-    #              for the IdP
-    #         * idp_brand: if specified in the IdP config, a textual identifier
-    #              for the brand of the IdP
-    #
-    # * HTML page shown after a successful user interactive authentication session:
-    #   'sso_auth_success.html'.
-    #
-    #   Note that this page must include the JavaScript which notifies of a successful authentication
-    #   (see https://matrix.org/docs/spec/client_server/r0.6.0#fallback).
-    #
-    #   This template has no additional variables.
-    #
-    # * HTML page shown after a user-interactive authentication session which
-    #   does not map correctly onto the expected user: 'sso_auth_bad_user.html'.
-    #
-    #   When rendering, this template is given the following variables:
-    #     * server_name: the homeserver's name.
-    #     * user_id_to_verify: the MXID of the user that we are trying to
-    #       validate.
-    #
-    # * HTML page shown during single sign-on if a deactivated user (according to Synapse's database)
-    #   attempts to login: 'sso_account_deactivated.html'.
-    #
-    #   This template has no additional variables.
-    #
-    # * HTML page to display to users if something goes wrong during the
-    #   OpenID Connect authentication process: 'sso_error.html'.
-    #
-    #   When rendering, this template is given two variables:
-    #     * error: the technical name of the error
-    #     * error_description: a human-readable message for the error
-    #
-    # You can see the default templates at:
-    # https://github.com/matrix-org/synapse/tree/master/synapse/res/templates
-    #
-    #template_dir: "res/templates"
-
 
 # JSON web token integration. The following settings can be used to make
 # Synapse JSON web tokens for authentication, instead of its internal
@@ -2220,6 +2073,9 @@ ui_auth:
 
 # Configuration for sending emails from Synapse.
 #
+# Server admins can configure custom templates for email content. See
+# https://matrix-org.github.io/synapse/latest/templates.html for more information.
+#
 email:
   # The hostname of the outgoing SMTP server to use. Defaults to 'localhost'.
   #
@@ -2296,49 +2152,6 @@ email:
   #
   #invite_client_location: https://app.element.io
 
-  # Directory in which Synapse will try to find the template files below.
-  # If not set, or the files named below are not found within the template
-  # directory, default templates from within the Synapse package will be used.
-  #
-  # Synapse will look for the following templates in this directory:
-  #
-  # * The contents of email notifications of missed events: 'notif_mail.html' and
-  #   'notif_mail.txt'.
-  #
-  # * The contents of account expiry notice emails: 'notice_expiry.html' and
-  #   'notice_expiry.txt'.
-  #
-  # * The contents of password reset emails sent by the homeserver:
-  #   'password_reset.html' and 'password_reset.txt'
-  #
-  # * An HTML page that a user will see when they follow the link in the password
-  #   reset email. The user will be asked to confirm the action before their
-  #   password is reset: 'password_reset_confirmation.html'
-  #
-  # * HTML pages for success and failure that a user will see when they confirm
-  #   the password reset flow using the page above: 'password_reset_success.html'
-  #   and 'password_reset_failure.html'
-  #
-  # * The contents of address verification emails sent during registration:
-  #   'registration.html' and 'registration.txt'
-  #
-  # * HTML pages for success and failure that a user will see when they follow
-  #   the link in an address verification email sent during registration:
-  #   'registration_success.html' and 'registration_failure.html'
-  #
-  # * The contents of address verification emails sent when an address is added
-  #   to a Matrix account: 'add_threepid.html' and 'add_threepid.txt'
-  #
-  # * HTML pages for success and failure that a user will see when they follow
-  #   the link in an address verification email sent when an address is added
-  #   to a Matrix account: 'add_threepid_success.html' and
-  #   'add_threepid_failure.html'
-  #
-  # You can see the default templates at:
-  # https://github.com/matrix-org/synapse/tree/master/synapse/res/templates
-  #
-  #template_dir: "res/templates"
-
   # Subjects to use when sending emails from Synapse.
   #
   # The placeholder '%(app)s' will be replaced with the value of the 'app_name'
diff --git a/docs/templates.md b/docs/templates.md
new file mode 100644
index 0000000000..a240f58b54
--- /dev/null
+++ b/docs/templates.md
@@ -0,0 +1,239 @@
+# Templates
+
+Synapse uses parametrised templates to generate the content of emails it sends and
+webpages it shows to users.
+
+By default, Synapse will use the templates listed [here](https://github.com/matrix-org/synapse/tree/master/synapse/res/templates).
+Server admins can configure an additional directory for Synapse to look for templates
+in, allowing them to specify custom templates:
+
+```yaml
+templates:
+  custom_templates_directory: /path/to/custom/templates/
+```
+
+If this setting is not set, or the files named below are not found within the directory,
+default templates from within the Synapse package will be used.
+
+Templates that are given variables when being rendered are rendered using [Jinja 2](https://jinja.palletsprojects.com/en/2.11.x/).
+Templates rendered by Jinja 2 can also access two functions on top of the functions
+already available as part of Jinja 2:
+
+```python
+format_ts(value: int, format: str) -> str
+```
+
+Formats a timestamp in milliseconds.
+
+Example: `reason.last_sent_ts|format_ts("%c")`
+
+```python
+mxc_to_http(value: str, width: int, height: int, resize_method: str = "crop") -> str
+```
+
+Turns a `mxc://` URL for media content into an HTTP(S) one using the homeserver's
+`public_baseurl` configuration setting as the URL's base.
+
+Example: `message.sender_avatar_url|mxc_to_http(32,32)`
+
+
+## Email templates
+
+Below are the templates Synapse will look for when generating the content of an email:
+
+* `notif_mail.html` and `notif_mail.txt`: The contents of email notifications of missed
+  events.
+  When rendering, this template is given the following variables:
+    * `user_display_name`: the display name for the user receiving the notification
+    * `unsubscribe_link`: the link users can click to unsubscribe from email notifications
+    * `summary_text`: a summary of the notification(s). The text used can be customised
+      by configuring the various settings in the `email.subjects` section of the
+      configuration file.
+    * `rooms`: a list of rooms containing events to include in the email. Each element is
+      an object with the following attributes:
+        * `title`: a human-readable name for the room
+        * `hash`: a hash of the ID of the room
+        * `invite`: a boolean, which is `True` if the room is an invite the user hasn't
+          accepted yet, `False` otherwise
+        * `notifs`: a list of events, or an empty list if `invite` is `True`. Each element
+          is an object with the following attributes:
+            * `link`: a `matrix.to` link to the event
+            * `ts`: the time in milliseconds at which the event was received
+            * `messages`: a list of messages containing one message before the event, the
+              message in the event, and one message after the event. Each element is an
+              object with the following attributes:
+                * `event_type`: the type of the event
+                * `is_historical`: a boolean, which is `False` if the message is the one
+                  that triggered the notification, `True` otherwise
+                * `id`: the ID of the event
+                * `ts`: the time in milliseconds at which the event was sent
+                * `sender_name`: the display name for the event's sender
+                * `sender_avatar_url`: the avatar URL (as a `mxc://` URL) for the event's
+                  sender
+                * `sender_hash`: a hash of the user ID of the sender
+        * `link`: a `matrix.to` link to the room
+    * `reason`: information on the event that triggered the email to be sent. It's an
+      object with the following attributes:
+        * `room_id`: the ID of the room the event was sent in
+        * `room_name`: a human-readable name for the room the event was sent in
+        * `now`: the current time in milliseconds
+        * `received_at`: the time in milliseconds at which the event was received
+        * `delay_before_mail_ms`: the amount of time in milliseconds Synapse always waits
+          before ever emailing about a notification (to give the user a chance to respond
+          to other push or notice the window)
+        * `last_sent_ts`: the time in milliseconds at which a notification was last sent
+          for an event in this room
+        * `throttle_ms`: the minimum amount of time in milliseconds between two
+          notifications can be sent for this room
+* `password_reset.html` and `password_reset.txt`: The contents of password reset emails
+  sent by the homeserver.
+  When rendering, these templates are given a `link` variable which contains the link the
+  user must click in order to reset their password.
+* `registration.html` and `registration.txt`: The contents of address verification emails
+  sent during registration.
+  When rendering, these templates are given a `link` variable which contains the link the
+  user must click in order to validate their email address.
+* `add_threepid.html` and `add_threepid.txt`: The contents of address verification emails
+  sent when an address is added to a Matrix account.
+  When rendering, these templates are given a `link` variable which contains the link the
+  user must click in order to validate their email address.
+
+
+## HTML page templates for registration and password reset
+
+Below are the templates Synapse will look for when generating pages related to
+registration and password reset:
+
+* `password_reset_confirmation.html`: An HTML page that a user will see when they follow
+  the link in the password reset email. The user will be asked to confirm the action
+  before their password is reset.
+  When rendering, this template is given the following variables:
+    * `sid`: the session ID for the password reset
+    * `token`: the token for the password reset
+    * `client_secret`: the client secret for the password reset
+* `password_reset_success.html` and `password_reset_failure.html`: HTML pages for success
+  and failure that a user will see when they confirm the password reset flow using the
+  page above.
+  When rendering, `password_reset_success.html` is given no variable, and
+  `password_reset_failure.html` is given a `failure_reason`, which contains the reason
+  for the password reset failure. 
+* `registration_success.html` and `registration_failure.html`: HTML pages for success and
+  failure that a user will see when they follow the link in an address verification email
+  sent during registration.
+  When rendering, `registration_success.html` is given no variable, and
+  `registration_failure.html` is given a `failure_reason`, which contains the reason
+  for the registration failure.
+* `add_threepid_success.html` and `add_threepid_failure.html`: HTML pages for success and
+  failure that a user will see when they follow the link in an address verification email
+  sent when an address is added to a Matrix account.
+  When rendering, `add_threepid_success.html` is given no variable, and
+  `add_threepid_failure.html` is given a `failure_reason`, which contains the reason
+  for the registration failure.
+
+
+## HTML page templates for Single Sign-On (SSO)
+
+Below are the templates Synapse will look for when generating pages related to SSO:
+
+* `sso_login_idp_picker.html`: HTML page to prompt the user to choose an
+  Identity Provider during login.
+  This is only used if multiple SSO Identity Providers are configured.
+  When rendering, this template is given the following variables:
+    * `redirect_url`: the URL that the user will be redirected to after
+      login.
+    * `server_name`: the homeserver's name.
+    * `providers`: a list of available Identity Providers. Each element is
+      an object with the following attributes:
+        * `idp_id`: unique identifier for the IdP
+        * `idp_name`: user-facing name for the IdP
+        * `idp_icon`: if specified in the IdP config, an MXC URI for an icon
+             for the IdP
+        * `idp_brand`: if specified in the IdP config, a textual identifier
+             for the brand of the IdP
+  The rendered HTML page should contain a form which submits its results
+  back as a GET request, with the following query parameters:
+    * `redirectUrl`: the client redirect URI (ie, the `redirect_url` passed
+      to the template)
+    * `idp`: the 'idp_id' of the chosen IDP.
+* `sso_auth_account_details.html`: HTML page to prompt new users to enter a
+  userid and confirm other details. This is only shown if the
+  SSO implementation (with any `user_mapping_provider`) does not return
+  a localpart.
+  When rendering, this template is given the following variables:
+    * `server_name`: the homeserver's name.
+    * `idp`: details of the SSO Identity Provider that the user logged in
+      with: an object with the following attributes:
+        * `idp_id`: unique identifier for the IdP
+        * `idp_name`: user-facing name for the IdP
+        * `idp_icon`: if specified in the IdP config, an MXC URI for an icon
+             for the IdP
+        * `idp_brand`: if specified in the IdP config, a textual identifier
+             for the brand of the IdP
+    * `user_attributes`: an object containing details about the user that
+      we received from the IdP. May have the following attributes:
+        * display_name: the user's display_name
+        * emails: a list of email addresses
+  The template should render a form which submits the following fields:
+    * `username`: the localpart of the user's chosen user id
+* `sso_new_user_consent.html`: HTML page allowing the user to consent to the
+  server's terms and conditions. This is only shown for new users, and only if
+  `user_consent.require_at_registration` is set.
+  When rendering, this template is given the following variables:
+    * `server_name`: the homeserver's name.
+    * `user_id`: the user's matrix proposed ID.
+    * `user_profile.display_name`: the user's proposed display name, if any.
+    * consent_version: the version of the terms that the user will be
+      shown
+    * `terms_url`: a link to the page showing the terms.
+  The template should render a form which submits the following fields:
+    * `accepted_version`: the version of the terms accepted by the user
+      (ie, 'consent_version' from the input variables).
+* `sso_redirect_confirm.html`: HTML page for a confirmation step before redirecting back
+  to the client with the login token.
+  When rendering, this template is given the following variables:
+    * `redirect_url`: the URL the user is about to be redirected to.
+    * `display_url`: the same as `redirect_url`, but with the query
+                   parameters stripped. The intention is to have a
+                   human-readable URL to show to users, not to use it as
+                   the final address to redirect to.
+    * `server_name`: the homeserver's name.
+    * `new_user`: a boolean indicating whether this is the user's first time
+         logging in.
+    * `user_id`: the user's matrix ID.
+    * `user_profile.avatar_url`: an MXC URI for the user's avatar, if any.
+          `None` if the user has not set an avatar.
+    * `user_profile.display_name`: the user's display name. `None` if the user
+          has not set a display name.
+* `sso_auth_confirm.html`: HTML page which notifies the user that they are authenticating
+  to confirm an operation on their account during the user interactive authentication
+  process.
+  When rendering, this template is given the following variables:
+    * `redirect_url`: the URL the user is about to be redirected to.
+    * `description`: the operation which the user is being asked to confirm
+    * `idp`: details of the Identity Provider that we will use to confirm
+      the user's identity: an object with the following attributes:
+        * `idp_id`: unique identifier for the IdP
+        * `idp_name`: user-facing name for the IdP
+        * `idp_icon`: if specified in the IdP config, an MXC URI for an icon
+             for the IdP
+        * `idp_brand`: if specified in the IdP config, a textual identifier
+             for the brand of the IdP
+* `sso_auth_success.html`: HTML page shown after a successful user interactive
+  authentication session.
+  Note that this page must include the JavaScript which notifies of a successful
+  authentication (see https://matrix.org/docs/spec/client_server/r0.6.0#fallback).
+  This template has no additional variables.
+* `sso_auth_bad_user.html`: HTML page shown after a user-interactive authentication
+  session which does not map correctly onto the expected user.
+  When rendering, this template is given the following variables:
+    * `server_name`: the homeserver's name.
+    * `user_id_to_verify`: the MXID of the user that we are trying to
+      validate.
+* `sso_account_deactivated.html`: HTML page shown during single sign-on if a deactivated
+  user (according to Synapse's database) attempts to login.
+  This template has no additional variables.
+* `sso_error.html`: HTML page to display to users if something goes wrong during the
+  OpenID Connect authentication process.
+  When rendering, this template is given two variables:
+    * `error`: the technical name of the error
+    * `error_description`: a human-readable message for the error
diff --git a/docs/upgrade.md b/docs/upgrade.md
index 8831c9d6cf..1c459d8e2b 100644
--- a/docs/upgrade.md
+++ b/docs/upgrade.md
@@ -112,6 +112,17 @@ environment variable.
 See [using a forward proxy with Synapse documentation](setup/forward_proxy.md) for
 details.
 
+## Deprecation of `template_dir`
+
+The `template_dir` settings in the `sso`, `account_validity` and `email` sections of the
+configuration file are now deprecated. Server admins should use the new
+`templates.custom_template_directory` setting in the configuration file and use one single
+custom template directory for all aforementioned features. Template file names remain
+unchanged. See [the related documentation](https://matrix-org.github.io/synapse/latest/templates.html)
+for more information and examples.
+
+We plan to remove support for these settings in October 2021.
+
 
 # Upgrading to v1.39.0