Modified /ws/join endpoint in order to return the remaining user id

include/rest-web-service.php

@@ -102,7 +102,7 @@ Flight::route('POST ' . $WS_PREFIX . '/user', function() {
 });
 
 /**
- * Perform a join.
+ * Performs a join.
  */
 Flight::route('POST ' . $WS_PREFIX . '/join', function() {
 
@@ -111,7 +111,8 @@ Flight::route('POST ' . $WS_PREFIX . '/join', function() {
 
     $userHandler->joinUsers($postData['user1'], $postData['user2']);
 
-    echo "Success";
+    // if the join has success, returns the remaining user id
+    echo $postData['user1'];
 });
 
 Flight::route('GET ' . $WS_PREFIX . '/test', function() {