Support 3PID login in password providers (#4931)

Adds a new method, check_3pid_auth, which gives password providers
the chance to allow authentication with third-party identifiers such
as email or msisdn.

synapse/module_api/__init__.py

@@ -73,14 +73,26 @@ class ModuleApi(object):
         """
         return self._auth_handler.check_user_exists(user_id)
 
-    def register(self, localpart):
-        """Registers a new user with given localpart
+    @defer.inlineCallbacks
+    def register(self, localpart, displayname=None):
+        """Registers a new user with given localpart and optional
+           displayname.
+
+        Args:
+            localpart (str): The localpart of the new user.
+            displayname (str|None): The displayname of the new user. If None,
+                the user's displayname will default to `localpart`.
 
         Returns:
             Deferred: a 2-tuple of (user_id, access_token)
         """
+        # Register the user
         reg = self.hs.get_registration_handler()
-        return reg.register(localpart=localpart)
+        user_id, access_token = yield reg.register(
+            localpart=localpart, default_display_name=displayname,
+        )
+
+        defer.returnValue((user_id, access_token))
 
     @defer.inlineCallbacks
     def invalidate_access_token(self, access_token):