title: Cloud Code Error - This user is not allowed to perform the get operation on _User
body: <p>I am using the master key but still see this error.</p>
  
  <blockquote>
    <p>Error: This user is not allowed to perform the get operation on _User. You can change this setting in the Data Browser. (Code: 119, Version: 1.2.19)</p>
  </blockquote>
  
  <p>This also seems to break a lot of other stuff like registration. I just want to make sure users can only change or set their username to something that does NOT start with a number and is alphanumeric. (compliant with channel names) </p>
  
  <pre><code>function usernameIsValid(username) {
      if (isNaN(parseInt(username[0])) &amp;&amp; username.match(/^[a-z0-9]+$/i)) {
          return true;
      } else {
          return false;
      }
  }
  Parse.Cloud.beforeSave(Parse.User, function(request, response) {
      Parse.Cloud.useMasterKey();
      if (usernameIsValid(request.object.get("username"))) {
          response.success();
      } else {
          response.error();
      }
  });
  </code></pre>