SSO Mapping Providers

A mapping provider is a Python class (loaded via a Python module) that works out how to map attributes of a SSO response 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.

SSO mapping providers are currently supported for OpenID and SAML SSO configurations. Please see the details below for how to implement your own.

It is up to the mapping provider whether the user should be assigned a predefined Matrix ID based on the SSO attributes, or if the user should be allowed to choose their own username.

In the first case - where users are automatically allocated a Matrix ID - it is the responsibility of the mapping provider to normalise the SSO attributes and map them to a valid Matrix ID. The specification for Matrix IDs has some information about what is considered valid.

If the mapping provider does not assign a Matrix ID, then Synapse will automatically serve an HTML page allowing the user to pick their own username.

External mapping providers are provided to Synapse in the form of an external Python module. You can retrieve this module from PyPI or elsewhere, but it must be importable via Synapse (e.g. it must be in the same virtualenv as Synapse). The Synapse config is then modified to point to the mapping provider (and optionally provide additional configuration for it).

OpenID Mapping Providers

The OpenID mapping provider can be customized by editing the oidc_config.user_mapping_provider.module config option.

oidc_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 OpenID Mapping Provider

A custom mapping provider must specify the following methods:

def __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.
def parse_config(config)
- This method should have the @staticmethod decoration.
- Arguments:
  - config - A dict representing the parsed content of the oidc_config.user_mapping_provider.config homeserver config option. Runs on homeserver startup. Providers should extract and validate any option values they need here.
- Whatever is returned will be passed back to the user mapping provider module's __init__ method during construction.
def get_remote_user_id(self, userinfo)
- Arguments:
  - userinfo - A authlib.oidc.core.claims.UserInfo object to extract user information from.
- This method must return a string, which is the unique, immutable identifier for the user. Commonly the sub claim of the response.
async def map_user_attributes(self, userinfo, token, failures)
- This method must be async.
- Arguments:
  - userinfo - A authlib.oidc.core.claims.UserInfo object to extract user information from.
  - token - A dictionary which includes information necessary to make further requests to the OpenID provider.
  - 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 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 localpart value, such as john.doe1.
- Returns a dictionary with two keys:
  - localpart: A string, used to generate the Matrix ID. If this is None, the user is prompted to pick their own username. This is only used during a user's first login. Once a localpart has been associated with a remote user ID (see get_remote_user_id) it cannot be updated.
  - displayname: An optional string, the display name for the user.
async def get_extra_attributes(self, userinfo, token)
- This method must be async.
- Arguments:
  - userinfo - A authlib.oidc.core.claims.UserInfo object to extract user information from.
  - token - A dictionary which includes information necessary to make further requests to the OpenID provider.
- Returns a dictionary that is suitable to be serialized to JSON. This will be returned as part of the response during a successful login.
  
  Note that care should be taken to not overwrite any of the parameters usually returned as part of the login response.

Default OpenID Mapping Provider

Synapse has a built-in OpenID mapping provider if a custom provider isn't specified in the config. It is located at synapse.handlers.oidc.JinjaOidcMappingProvider.

SAML Mapping Providers

The SAML mapping provider can be customized 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 SAML Mapping Provider

A custom mapping provider must specify the following methods:

def __init__(self, parsed_config, module_api)
- 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.
  - module_api - a synapse.module_api.ModuleApi object which provides the stable API available for extension modules.
def parse_config(config)
- This method should have the @staticmethod decoration.
- Arguments:
  - config - A dict representing the parsed content of the saml_config.user_mapping_provider.config homeserver config option. Runs on homeserver startup. Providers should extract and validate any option values they need here.
- Whatever is returned will be passed back to the user mapping provider module's __init__ method during construction.
def 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.
def get_remote_user_id(self, saml_response, client_redirect_url)
- Arguments:
  - saml_response - A saml2.response.AuthnResponse object to extract user information from.
  - client_redirect_url - A string, the URL that the client will be redirected to.
- This method must return a string, which is the unique, immutable identifier for the user. Commonly the uid claim of the response.
def saml_response_to_user_attributes(self, saml_response, failures, client_redirect_url)
- 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.
  - client_redirect_url - A string, the URL that the client will be redirected to.
- 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 - A string, the mxid localpart of the new user. If this is None, the user is prompted to pick their own username. This is only used during a user's first login. Once a localpart has been associated with a remote user ID (see get_remote_user_id) it cannot be updated.
  - displayname - The displayname of the new user. If not provided, will default to the value of mxid_localpart.
  - emails - A list of emails for the new user. If not provided, will default to an empty list.
  Alternatively it can raise a synapse.api.errors.RedirectException to redirect the user to another page. This is useful to prompt the user for additional information, e.g. if you want them to provide their own username. It is the responsibility of the mapping provider to either redirect back to client_redirect_url (including any additional information) or to complete registration using methods from the ModuleApi.

Default SAML Mapping 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.DefaultSamlMappingProvider.

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