title: Restricting URL so that only web application can access it (firebase + google app engine)
body: <p>I was wondering if it was possible to restrict a URL so that only your web application can query it.</p>
  
  <p>I want to store a list of used usernames so that when a user signs up, I can check if the username they want to use is unique.</p>
  
  <p>I am storing my usernames both in a FIREBASE and Google App Engine data store.</p>
  
  <p>I was wondering if it was possible to restrict the URL that my server queries (e.g. /usernames) so that ONLY my server can query it. That is, if someone goes to the URL usernames, they'll just be redirected back to the home page or something.</p>
  
  <p>Thanks in advance</p>