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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_3pid_auth`(*medium*, *address*, *password*)
+
+> This method, if implemented, is called when a user attempts to
+> register or log in with a third party identifier, such as email. It is
+> passed the medium (ex. "email"), an address (ex.
+> "<jdoe@example.com>") and the user's password.
+>
+> The method should return a Twisted `Deferred` object, which resolves
+> to a `str` containing the user's (canonical) User ID if
+> authentication was successful, and `None` if not.
+>
+> As with `check_auth`, the `Deferred` may alternatively resolve to a
+> `(user_id, callback)` tuple.
+
+`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.