diff --git a/synapse/module_api/__init__.py b/synapse/module_api/__init__.py
index 305b9b0178..d680ee95e1 100644
--- a/synapse/module_api/__init__.py
+++ b/synapse/module_api/__init__.py
@@ -1,5 +1,6 @@
 # -*- coding: utf-8 -*-
 # Copyright 2017 New Vector Ltd
+# Copyright 2020 The Matrix.org Foundation C.I.C.
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
 # you may not use this file except in compliance with the License.
@@ -16,18 +17,26 @@ import logging
 
 from twisted.internet import defer
 
+from synapse.logging.context import make_deferred_yieldable, run_in_background
 from synapse.types import UserID
 
+"""
+This package defines the 'stable' API which can be used by extension modules which
+are loaded into Synapse.
+"""
+
+__all__ = ["errors", "make_deferred_yieldable", "run_in_background", "ModuleApi"]
+
 logger = logging.getLogger(__name__)
 
 
 class ModuleApi(object):
-    """A proxy object that gets passed to password auth providers so they
+    """A proxy object that gets passed to various plugin modules so they
     can register new users etc if necessary.
     """
 
     def __init__(self, hs, auth_handler):
-        self.hs = hs
+        self._hs = hs
 
         self._store = hs.get_datastore()
         self._auth = hs.get_auth()
@@ -64,7 +73,7 @@ class ModuleApi(object):
         """
         if username.startswith("@"):
             return username
-        return UserID(username, self.hs.hostname).to_string()
+        return UserID(username, self._hs.hostname).to_string()
 
     def check_user_exists(self, user_id):
         """Check if user exists.
@@ -111,10 +120,14 @@ class ModuleApi(object):
             displayname (str|None): The displayname of the new user.
             emails (List[str]): Emails to bind to the new user.
 
+        Raises:
+            SynapseError if there is an error performing the registration. Check the
+                'errcode' property for more information on the reason for failure
+
         Returns:
             Deferred[str]: user_id
         """
-        return self.hs.get_registration_handler().register_user(
+        return self._hs.get_registration_handler().register_user(
             localpart=localpart, default_display_name=displayname, bind_emails=emails
         )
 
@@ -131,12 +144,34 @@ class ModuleApi(object):
         Returns:
             defer.Deferred[tuple[str, str]]: Tuple of device ID and access token
         """
-        return self.hs.get_registration_handler().register_device(
+        return self._hs.get_registration_handler().register_device(
             user_id=user_id,
             device_id=device_id,
             initial_display_name=initial_display_name,
         )
 
+    def record_user_external_id(
+        self, auth_provider_id: str, remote_user_id: str, registered_user_id: str
+    ) -> defer.Deferred:
+        """Record a mapping from an external user id to a mxid
+
+        Args:
+            auth_provider: identifier for the remote auth provider
+            external_id: id on that system
+            user_id: complete mxid that it is mapped to
+        """
+        return self._store.record_user_external_id(
+            auth_provider_id, remote_user_id, registered_user_id
+        )
+
+    def generate_short_term_login_token(
+        self, user_id: str, duration_in_ms: int = (2 * 60 * 1000)
+    ) -> str:
+        """Generate a login token suitable for m.login.token authentication"""
+        return self._hs.get_macaroon_generator().generate_short_term_login_token(
+            user_id, duration_in_ms
+        )
+
     @defer.inlineCallbacks
     def invalidate_access_token(self, access_token):
         """Invalidate an access token for a user
@@ -157,7 +192,7 @@ class ModuleApi(object):
         user_id = user_info["user"].to_string()
         if device_id:
             # delete the device, which will also delete its access tokens
-            yield self.hs.get_device_handler().delete_device(user_id, device_id)
+            yield self._hs.get_device_handler().delete_device(user_id, device_id)
         else:
             # no associated device. Just delete the access token.
             yield self._auth_handler.delete_access_token(access_token)
diff --git a/synapse/module_api/errors.py b/synapse/module_api/errors.py
new file mode 100644
index 0000000000..b15441772c
--- /dev/null
+++ b/synapse/module_api/errors.py
@@ -0,0 +1,18 @@
+# -*- coding: utf-8 -*-
+# Copyright 2020 The Matrix.org Foundation C.I.C.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""Exception types which are exposed as part of the stable module API"""
+
+from synapse.api.errors import RedirectException, SynapseError  # noqa: F401