diff --git a/docs/saml_mapping_providers.md b/docs/saml_mapping_providers.md
new file mode 100644
index 0000000000..92f2380488
--- /dev/null
+++ b/docs/saml_mapping_providers.md
@@ -0,0 +1,77 @@
+# SAML Mapping Providers
+
+A SAML mapping provider is a Python class (loaded via a Python module) that
+works out how to map attributes of a SAML response object to Matrix-specific
+user attributes. Details such as user ID localpart, displayname, and even avatar
+URLs are all things that can be mapped from talking to a SSO service.
+
+As an example, a SSO service may return the email address
+"john.smith@example.com" for a user, whereas Synapse will need to figure out how
+to turn that into a displayname when creating a Matrix user for this individual.
+It may choose `John Smith`, or `Smith, John [Example.com]` or any number of
+variations. As each Synapse configuration may want something different, this is
+where SAML mapping providers come into play.
+
+## Enabling Providers
+
+External mapping providers are provided to Synapse in the form of an external
+Python module. Retrieve this module from [PyPi](https://pypi.org) or elsewhere,
+then tell Synapse where to look for the handler class by editing the
+`saml2_config.user_mapping_provider.module` config option.
+
+`saml2_config.user_mapping_provider.config` allows you to provide custom
+configuration options to the module. Check with the module's documentation for
+what options it provides (if any). The options listed by default are for the
+user mapping provider built in to Synapse. If using a custom module, you should
+comment these options out and use those specified by the module instead.
+
+## Building a Custom Mapping Provider
+
+A custom mapping provider must specify the following methods:
+
+* `__init__(self, parsed_config)`
+ - Arguments:
+ - `parsed_config` - A configuration object that is the return value of the
+ `parse_config` method. You should set any configuration options needed by
+ the module here.
+* `saml_response_to_user_attributes(self, saml_response, failures)`
+ - Arguments:
+ - `saml_response` - A `saml2.response.AuthnResponse` object to extract user
+ information from.
+ - `failures` - An `int` that represents the amount of times the returned
+ mxid localpart mapping has failed. This should be used
+ to create a deduplicated mxid localpart which should be
+ returned instead. For example, if this method returns
+ `john.doe` as the value of `mxid_localpart` in the returned
+ dict, and that is already taken on the homeserver, this
+ method will be called again with the same parameters but
+ with failures=1. The method should then return a different
+ `mxid_localpart` value, such as `john.doe1`.
+ - This method must return a dictionary, which will then be used by Synapse
+ to build a new user. The following keys are allowed:
+ * `mxid_localpart` - Required. The mxid localpart of the new user.
+ * `displayname` - The displayname of the new user. If not provided, will default to
+ the value of `mxid_localpart`.
+* `parse_config(config)`
+ - This method should have the `@staticmethod` decoration.
+ - Arguments:
+ - `config` - A `dict` representing the parsed content of the
+ `saml2_config.user_mapping_provider.config` homeserver config option.
+ Runs on homeserver startup. Providers should extract any option values
+ they need here.
+ - Whatever is returned will be passed back to the user mapping provider module's
+ `__init__` method during construction.
+* `get_saml_attributes(config)`
+ - This method should have the `@staticmethod` decoration.
+ - Arguments:
+ - `config` - A object resulting from a call to `parse_config`.
+ - Returns a tuple of two sets. The first set equates to the saml auth
+ response attributes that are required for the module to function, whereas
+ the second set consists of those attributes which can be used if available,
+ but are not necessary.
+
+## Synapse's Default Provider
+
+Synapse has a built-in SAML mapping provider if a custom provider isn't
+specified in the config. It is located at
+[`synapse.handlers.saml_handler.DefaultSamlMappingProvider`](../synapse/handlers/saml_handler.py).
diff --git a/docs/sample_config.yaml b/docs/sample_config.yaml
index 10664ae8f7..4d44e631d1 100644
--- a/docs/sample_config.yaml
+++ b/docs/sample_config.yaml
@@ -1250,33 +1250,58 @@ saml2_config:
#
#config_path: "CONFDIR/sp_conf.py"
- # the lifetime of a SAML session. This defines how long a user has to
+ # 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 5 minutes.
#
#saml_session_lifetime: 5m
- # The SAML attribute (after mapping via the attribute maps) to use to derive
- # the Matrix ID from. 'uid' by default.
+ # An external module can be provided here as a custom solution to
+ # mapping attributes returned from a saml provider onto a matrix user.
#
- #mxid_source_attribute: displayName
-
- # The mapping system to use for mapping the saml attribute onto a matrix ID.
- # Options include:
- # * 'hexencode' (which maps unpermitted characters to '=xx')
- # * 'dotreplace' (which replaces unpermitted characters with '.').
- # The default is 'hexencode'.
- #
- #mxid_mapping: dotreplace
+ user_mapping_provider:
+ # The custom module's class. Uncomment to use a custom module.
+ #
+ #module: mapping_provider.SamlMappingProvider
- # 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.
+ # Custom configuration values for the module. Below options are
+ # intended for the built-in provider, they should be changed if
+ # using a custom module. This section will be passed as a Python
+ # dictionary to the module's `parse_config` method.
+ #
+ config:
+ # The SAML attribute (after mapping via the attribute maps) to use
+ # to derive the Matrix ID from. '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_source_attribute: displayName
+
+ # The mapping system to use for mapping the saml attribute onto a
+ # matrix ID.
+ #
+ # Options include:
+ # * 'hexencode' (which maps unpermitted characters to '=xx')
+ # * '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.
+ #
+ #mxid_mapping: dotreplace
+
+ # 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.
+ # 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'.
#
|
