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+Password auth provider modules
+==============================
+
+Password auth providers offer a way for server administrators to integrate
+their Synapse installation with an existing authentication system.
+
+A password auth provider is a Python class which is dynamically loaded into
+Synapse, and provides a number of methods by which it can integrate with the
+authentication system.
+
+This document serves as a reference for those looking to implement their own
+password auth providers.
+
+Required methods
+----------------
+
+Password auth provider classes must provide the following methods:
+
+*class* ``SomeProvider.parse_config``\(*config*)
+
+    This method is passed the ``config`` object for this module from the
+    homeserver configuration file.
+
+    It should perform any appropriate sanity checks on the provided
+    configuration, and return an object which is then passed into ``__init__``.
+
+*class* ``SomeProvider``\(*config*, *account_handler*)
+
+    The constructor is passed the config object returned by ``parse_config``,
+    and a ``synapse.module_api.ModuleApi`` object which allows the
+    password provider to check if accounts exist and/or create new ones.
+
+Optional methods
+----------------
+
+Password auth provider classes may optionally provide the following methods.
+
+*class* ``SomeProvider.get_db_schema_files``\()
+
+    This method, if implemented, should return an Iterable of ``(name,
+    stream)`` pairs of database schema files. Each file is applied in turn at
+    initialisation, and a record is then made in the database so that it is
+    not re-applied on the next start.
+
+``someprovider.get_supported_login_types``\()
+
+    This method, if implemented, should return a ``dict`` mapping from a login
+    type identifier (such as ``m.login.password``) to an iterable giving the
+    fields which must be provided by the user in the submission to the
+    ``/login`` api. These fields are passed in the ``login_dict`` dictionary
+    to ``check_auth``.
+
+    For example, if a password auth provider wants to implement a custom login
+    type of ``com.example.custom_login``, where the client is expected to pass
+    the fields ``secret1`` and ``secret2``, the provider should implement this
+    method and return the following dict::
+
+      {"com.example.custom_login": ("secret1", "secret2")}
+
+``someprovider.check_auth``\(*username*, *login_type*, *login_dict*)
+
+    This method is the one that does the real work. If implemented, it will be
+    called for each login attempt where the login type matches one of the keys
+    returned by ``get_supported_login_types``.
+
+    It is passed the (possibly UNqualified) ``user`` provided by the client,
+    the login type, and a dictionary of login secrets passed by the client.
+
+    The method should return a Twisted ``Deferred`` object, which resolves to
+    the canonical ``@localpart:domain`` user id if authentication is successful,
+    and ``None`` if not.
+
+    Alternatively, the ``Deferred`` can resolve to a ``(str, func)`` tuple, in
+    which case the second field is a callback which will be called with the
+    result from the ``/login`` call (including ``access_token``, ``device_id``,
+    etc.)
+
+``someprovider.check_password``\(*user_id*, *password*)
+
+    This method provides a simpler interface than ``get_supported_login_types``
+    and ``check_auth`` for password auth providers that just want to provide a
+    mechanism for validating ``m.login.password`` logins.
+
+    Iif implemented, it will be called to check logins with an
+    ``m.login.password`` login type. It is passed a qualified
+    ``@localpart:domain`` user id, and the password provided by the user.
+
+    The method should return a Twisted ``Deferred`` object, which resolves to
+    ``True`` if authentication is successful, and ``False`` if not.
+
+``someprovider.on_logged_out``\(*user_id*, *device_id*, *access_token*)
+
+    This method, if implemented, is called when a user logs out. It is passed
+    the qualified user ID, the ID of the deactivated device (if any: access
+    tokens are occasionally created without an associated device ID), and the
+    (now deactivated) access token.
+
+    It may return a Twisted ``Deferred`` object; the logout request will wait
+    for the deferred to complete but the result is ignored.