Add admin API for logging in as a user (#8617)

synapse/rest/admin/users.py

@@ -16,7 +16,7 @@ import hashlib
 import hmac
 import logging
 from http import HTTPStatus
-from typing import Tuple
+from typing import TYPE_CHECKING, Tuple
 
 from synapse.api.constants import UserTypes
 from synapse.api.errors import Codes, NotFoundError, SynapseError
@@ -37,6 +37,9 @@ from synapse.rest.admin._base import (
 )
 from synapse.types import JsonDict, UserID
 
+if TYPE_CHECKING:
+    from synapse.server import HomeServer
+
 logger = logging.getLogger(__name__)
 
 _GET_PUSHERS_ALLOWED_KEYS = {
@@ -828,3 +831,52 @@ class UserMediaRestServlet(RestServlet):
             ret["next_token"] = start + len(media)
 
         return 200, ret
+
+
+class UserTokenRestServlet(RestServlet):
+    """An admin API for logging in as a user.
+
+    Example:
+
+        POST /_synapse/admin/v1/users/@test:example.com/login
+        {}
+
+        200 OK
+        {
+            "access_token": "<some_token>"
+        }
+    """
+
+    PATTERNS = admin_patterns("/users/(?P<user_id>[^/]*)/login$")
+
+    def __init__(self, hs: "HomeServer"):
+        self.hs = hs
+        self.store = hs.get_datastore()
+        self.auth = hs.get_auth()
+        self.auth_handler = hs.get_auth_handler()
+
+    async def on_POST(self, request, user_id):
+        requester = await self.auth.get_user_by_req(request)
+        await assert_user_is_admin(self.auth, requester.user)
+        auth_user = requester.user
+
+        if not self.hs.is_mine_id(user_id):
+            raise SynapseError(400, "Only local users can be logged in as")
+
+        body = parse_json_object_from_request(request, allow_empty_body=True)
+
+        valid_until_ms = body.get("valid_until_ms")
+        if valid_until_ms and not isinstance(valid_until_ms, int):
+            raise SynapseError(400, "'valid_until_ms' parameter must be an int")
+
+        if auth_user.to_string() == user_id:
+            raise SynapseError(400, "Cannot use admin API to login as self")
+
+        token = await self.auth_handler.get_access_token_for_user_id(
+            user_id=auth_user.to_string(),
+            device_id=None,
+            valid_until_ms=valid_until_ms,
+            puppets_user_id=user_id,
+        )
+
+        return 200, {"access_token": token}