diff --git a/lib/client.js b/lib/client.js
index 5e57a75db..93e494aea 100644
--- a/lib/client.js
+++ b/lib/client.js
@@ -661,31 +661,50 @@ MatrixClient.prototype.joinRoom = function(roomIdOrAlias, opts, callback) {
     if (utils.isFunction(opts)) {
         throw new Error("Expected 'opts' object, got function.");
     }
-    opts = opts || {
-        syncRoom: true
-    };
+    opts = opts || {};
+    if (opts.syncRoom === undefined) { opts.syncRoom = true; }
 
     var room = this.getRoom(roomIdOrAlias);
     if (room && room.hasMembershipState(this.credentials.userId, "join")) {
         return q(room);
     }
-    var path = utils.encodeUri("/join/$roomid", { $roomid: roomIdOrAlias});
+
+    var sign_promise = q();
+
+    if (opts.inviteSignUrl) {
+        sign_promise = this._http.requestOtherUrl(
+            undefined, 'POST',
+            opts.inviteSignUrl, { mxid: this.credentials.userId }
+        );
+    }
+
     var defer = q.defer();
+
     var self = this;
-    this._http.authedRequest(undefined, "POST", path, undefined, {}).then(
-    function(res) {
-        var roomId = res.room_id;
-        var syncApi = new SyncApi(self);
-        var room = syncApi.createRoom(roomId);
-        if (opts.syncRoom) {
-            // v2 will do this for us
-            // return syncApi.syncRoom(room);
+    sign_promise.done(function(signed_invite_object) {
+        var data = {};
+        if (signed_invite_object) {
+            data.third_party_signed = signed_invite_object;
         }
-        return q(room);
-    }, function(err) {
-        _reject(callback, defer, err);
-    }).done(function(room) {
-        _resolve(callback, defer, room);
+
+        var path = utils.encodeUri("/join/$roomid", { $roomid: roomIdOrAlias});
+        self._http.authedRequest(undefined, "POST", path, undefined, data).then(
+        function(res) {
+            var roomId = res.room_id;
+            var syncApi = new SyncApi(self);
+            var room = syncApi.createRoom(roomId);
+            if (opts.syncRoom) {
+                // v2 will do this for us
+                // return syncApi.syncRoom(room);
+            }
+            return q(room);
+        }, function(err) {
+            _reject(callback, defer, err);
+        }).done(function(room) {
+            _resolve(callback, defer, room);
+        }, function(err) {
+            _reject(callback, defer, err);
+        });
     }, function(err) {
         _reject(callback, defer, err);
     });
diff --git a/lib/http-api.js b/lib/http-api.js
index a3ab93cfa..3b3bb124d 100644
--- a/lib/http-api.js
+++ b/lib/http-api.js
@@ -365,6 +365,34 @@ module.exports.MatrixHttpApi.prototype = {
         );
     },
 
+    /**
+     * Perform a request to an arbitrary URL.
+     * @param {Function} callback Optional. The callback to invoke on
+     * success/failure. See the promise return values for more information.
+     * @param {string} method The HTTP method e.g. "GET".
+     * @param {string} uri The HTTP URI
+     * @param {Object} queryParams A dict of query params (these will NOT be
+     * urlencoded).
+     * @param {Object} data The HTTP JSON body.
+     * @param {Number=} localTimeoutMs The maximum amount of time to wait before
+     * timing out the request. If not specified, there is no timeout.
+     * @return {module:client.Promise} Resolves to <code>{data: {Object},
+     * headers: {Object}, code: {Number}}</code>.
+     * If <code>onlyData</code> is set, this will resolve to the <code>data</code>
+     * object only.
+     * @return {module:http-api.MatrixError} Rejects with an error if a problem
+     * occurred. This includes network problems and Matrix-specific error JSON.
+     */
+    requestOtherUrl: function(callback, method, uri, queryParams, data,
+                                localTimeoutMs) {
+        if (!queryParams) {
+            queryParams = {};
+        }
+        return this._request(
+            callback, method, uri, queryParams, data, localTimeoutMs
+        );
+    },
+
     /**
      * Form and return a homeserver request URL based on the given path
      * params and prefix.