Implementation of MSC3882 login token request

changelog.d/13722.misc

@@ -0,0 +1 @@
+Experimental implementation of MSC3882 to allow an existing device/session to generate a login token for use on a new device/session.

synapse/config/experimental.py

@@ -93,3 +93,10 @@ def read_config(self, config: JsonDict, **kwargs: Any) -> None:
 
         # MSC3852: Expose last seen user agent field on /_matrix/client/v3/devices.
         self.msc3852_enabled: bool = experimental.get("msc3852_enabled", False)
+
+        # MSC3882: Allow an existing session to sign in a new session
+        self.msc3882_enabled: bool = experimental.get("msc3882_enabled", False)
+        self.msc3882_ui_auth: bool = experimental.get("msc3882_ui_auth", True)
+        self.msc3882_token_timeout = self.parse_duration(
+            experimental.get("msc3882_token_timeout", "5m")
+        )

synapse/rest/__init__.py

@@ -30,6 +30,7 @@
     keys,
     knock,
     login as v1_login,
+    login_token_request,
     logout,
     mutual_rooms,
     notifications,
@@ -130,3 +131,4 @@ def register_servlets(client_resource: HttpServer, hs: "HomeServer") -> None:
 
         # unstable
         mutual_rooms.register_servlets(hs, client_resource)
+        login_token_request.register_servlets(hs, client_resource)

synapse/rest/client/login_token_request.py

@@ -0,0 +1,101 @@
+# Copyright 2022 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.
+
+import logging
+from typing import TYPE_CHECKING, Tuple
+
+from synapse.http.server import HttpServer
+from synapse.http.servlet import RestServlet, parse_json_object_from_request
+from synapse.http.site import SynapseRequest
+from synapse.types import JsonDict
+from synapse.util.stringutils import random_string
+
+from ._base import client_patterns, interactive_auth_handler
+
+if TYPE_CHECKING:
+    from synapse.server import HomeServer
+
+logger = logging.getLogger(__name__)
+
+
+class LoginTokenRequestServlet(RestServlet):
+    """
+    Get a token that can be used with `m.login.token` to log in a second device.
+
+    Request:
+
+    POST /login/token?access_token=... HTTP/1.1
+
+    {}
+
+    Response:
+
+    HTTP/1.1 200 OK
+    {
+        "login_token": "ABDEFGH",
+        "expires_in": 3600,
+    }
+    """
+
+    PATTERNS = client_patterns("/login/token$")
+
+    def __init__(self, hs: "HomeServer"):
+        super().__init__()
+        self.auth = hs.get_auth()
+        self.store = hs.get_datastores().main
+        self.clock = hs.get_clock()
+        self.server_name = hs.config.server.server_name
+        self.macaroon_gen = hs.get_macaroon_generator()
+        self.auth_handler = hs.get_auth_handler()
+        self.token_timeout = hs.config.experimental.msc3882_token_timeout
+        self.ui_auth = hs.config.experimental.msc3882_ui_auth
+
+    @interactive_auth_handler
+    async def on_POST(self, request: SynapseRequest) -> Tuple[int, JsonDict]:
+        requester = await self.auth.get_user_by_req(request)
+        user_id = requester.user.to_string()
+        body = parse_json_object_from_request(request)
+
+        if self.ui_auth:
+            await self.auth_handler.validate_user_via_ui_auth(
+                requester,
+                request,
+                body,
+                "issue a new access token for your account",
+                can_skip_ui_auth=False,  # Don't allow skipping of UI auth
+            )
+
+        token = random_string(24)
+        ts_valid_until_ms = self.clock.time_msec() + self.token_timeout
+
+        login_token = self.macaroon_gen.generate_short_term_login_token(
+            user_id=requester.user.to_string(),
+            auth_provider_id="org.matrix.msc3882.login_token_request",
+            duration_in_ms=self.token_timeout,
+        )
+
+        await self.store.insert_open_id_token(token, ts_valid_until_ms, user_id)
+
+        return (
+            200,
+            {
+                "login_token": login_token,
+                "expires_in": self.token_timeout // 1000,
+            },
+        )
+
+
+def register_servlets(hs: "HomeServer", http_server: HttpServer) -> None:
+    if hs.config.experimental.msc3882_enabled:
+        LoginTokenRequestServlet(hs).register(http_server)

synapse/rest/client/versions.py

@@ -105,6 +105,8 @@ def on_GET(self, request: Request) -> Tuple[int, JsonDict]:
                     "org.matrix.msc3440.stable": True,  # TODO: remove when "v1.3" is added above
                     # Allows moderators to fetch redacted event content as described in MSC2815
                     "fi.mau.msc2815": self.config.experimental.msc2815_enabled,
+                    # Adds support for login token requests as per MSC3882
+                    "org.matrix.msc3882": self.config.experimental.msc3882_enabled,
                 },
             },
         )