Add device_id support to /login

Add a 'devices' table to the storage, as well as a 'device_id' column to
refresh_tokens.

Allow the client to pass a device_id, and initial_device_display_name, to
/login. If login is successful, then register the device in the devices table
if it wasn't known already. If no device_id was supplied, make one up.

Associate the device_id with the access token and refresh token, so that we can
get at it again later. Ensure that the device_id is copied from the refresh
token to the access_token when the token is refreshed.

synapse/handlers/device.py

@@ -0,0 +1,71 @@
+# -*- coding: utf-8 -*-
+# Copyright 2016 OpenMarket Ltd
+#
+# 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.
+from synapse.api.errors import StoreError
+from synapse.util import stringutils
+from twisted.internet import defer
+from ._base import BaseHandler
+
+import logging
+
+logger = logging.getLogger(__name__)
+
+
+class DeviceHandler(BaseHandler):
+    def __init__(self, hs):
+        super(DeviceHandler, self).__init__(hs)
+
+    @defer.inlineCallbacks
+    def check_device_registered(self, user_id, device_id,
+                                initial_device_display_name):
+        """
+        If the given device has not been registered, register it with the
+        supplied display name.
+
+        If no device_id is supplied, we make one up.
+
+        Args:
+            user_id (str):  @user:id
+            device_id (str | None): device id supplied by client
+            initial_device_display_name (str | None): device display name from
+                 client
+        Returns:
+            str: device id (generated if none was supplied)
+        """
+        if device_id is not None:
+            yield self.store.store_device(
+                user_id=user_id,
+                device_id=device_id,
+                initial_device_display_name=initial_device_display_name,
+                ignore_if_known=True,
+            )
+            defer.returnValue(device_id)
+
+        # if the device id is not specified, we'll autogen one, but loop a few
+        # times in case of a clash.
+        attempts = 0
+        while attempts < 5:
+            try:
+                device_id = stringutils.random_string_with_symbols(16)
+                yield self.store.store_device(
+                    user_id=user_id,
+                    device_id=device_id,
+                    initial_device_display_name=initial_device_display_name,
+                    ignore_if_known=False,
+                )
+                defer.returnValue(device_id)
+            except StoreError:
+                attempts += 1
+
+        raise StoreError(500, "Couldn't generate a device ID.")