Add POST submit_token endpoint for MSISDN (#6078)

First part of solving #6076

changelog.d/6078.feature

@@ -0,0 +1 @@
+Add `POST /add_threepid/msisdn/submit_token` endpoint for proxying submitToken on an account_threepid_handler.

synapse/handlers/identity.py

@@ -491,6 +491,40 @@ def validate_threepid_session(self, client_secret, sid):
 
         return validation_session
 
+    @defer.inlineCallbacks
+    def proxy_msisdn_submit_token(self, id_server, client_secret, sid, token):
+        """Proxy a POST submitToken request to an identity server for verification purposes
+
+        Args:
+            id_server (str): The identity server URL to contact
+
+            client_secret (str): Secret provided by the client
+
+            sid (str): The ID of the session
+
+            token (str): The verification token
+
+        Raises:
+            SynapseError: If we failed to contact the identity server
+
+        Returns:
+            Deferred[dict]: The response dict from the identity server
+        """
+        body = {"client_secret": client_secret, "sid": sid, "token": token}
+
+        try:
+            return (
+                yield self.http_client.post_json_get_json(
+                    id_server + "/_matrix/identity/api/v1/validate/msisdn/submitToken",
+                    body,
+                )
+            )
+        except TimeoutError:
+            raise SynapseError(500, "Timed out contacting identity server")
+        except HttpResponseException as e:
+            logger.warning("Error contacting msisdn account_threepid_delegate: %s", e)
+            raise SynapseError(400, "Error contacting the identity server")
+
 
 def create_id_access_token_header(id_access_token):
     """Create an Authorization header for passing to SimpleHttpClient as the header value

synapse/rest/client/v2_alpha/account.py

@@ -524,7 +524,7 @@ def on_POST(self, request):
         return 200, ret
 
 
-class AddThreepidSubmitTokenServlet(RestServlet):
+class AddThreepidEmailSubmitTokenServlet(RestServlet):
     """Handles 3PID validation token submission for adding an email to a user's account"""
 
     PATTERNS = client_patterns(
@@ -600,6 +600,48 @@ def on_GET(self, request):
         finish_request(request)
 
 
+class AddThreepidMsisdnSubmitTokenServlet(RestServlet):
+    """Handles 3PID validation token submission for adding a phone number to a user's
+    account
+    """
+
+    PATTERNS = client_patterns(
+        "/add_threepid/msisdn/submit_token$", releases=(), unstable=True
+    )
+
+    def __init__(self, hs):
+        """
+        Args:
+            hs (synapse.server.HomeServer): server
+        """
+        super().__init__()
+        self.config = hs.config
+        self.clock = hs.get_clock()
+        self.store = hs.get_datastore()
+        self.identity_handler = hs.get_handlers().identity_handler
+
+    @defer.inlineCallbacks
+    def on_POST(self, request):
+        if not self.config.account_threepid_delegate_msisdn:
+            raise SynapseError(
+                400,
+                "This homeserver is not validating phone numbers. Use an identity server "
+                "instead.",
+            )
+
+        body = parse_json_object_from_request(request)
+        assert_params_in_dict(body, ["client_secret", "sid", "token"])
+
+        # Proxy submit_token request to msisdn threepid delegate
+        response = yield self.identity_handler.proxy_msisdn_submit_token(
+            self.config.account_threepid_delegate_msisdn,
+            body["client_secret"],
+            body["sid"],
+            body["token"],
+        )
+        return 200, response
+
+
 class ThreepidRestServlet(RestServlet):
     PATTERNS = client_patterns("/account/3pid$")
 
@@ -807,7 +849,8 @@ def register_servlets(hs, http_server):
     DeactivateAccountRestServlet(hs).register(http_server)
     EmailThreepidRequestTokenRestServlet(hs).register(http_server)
     MsisdnThreepidRequestTokenRestServlet(hs).register(http_server)
-    AddThreepidSubmitTokenServlet(hs).register(http_server)
+    AddThreepidEmailSubmitTokenServlet(hs).register(http_server)
+    AddThreepidMsisdnSubmitTokenServlet(hs).register(http_server)
     ThreepidRestServlet(hs).register(http_server)
     ThreepidAddRestServlet(hs).register(http_server)
     ThreepidBindRestServlet(hs).register(http_server)