title: Authenticate a user from a page tab
body: <p>I'm trying to make a Facebook page tab where people can vote for their favorite video or music track from a bunch of embedded files. I need to get a unique ID from each user to make sure that they can only vote once. The signed_request only contains the user's id if they have authorized my app.</p>
  <p>I have tried to have users authorize my app using the FB.login() javascript api, but I get the error:</p>
  <blockquote>
  <p><strong>An error occurred with Remix // Rework Vote. Please try later</strong></p>
  <p>API Error Code: 191</p>
  <p>API Error Description: The specified URL is not owned by the application</p>
  <p>Error Message: Invalid redirect_uri: Given URL is not permitted by the application configuration.</p>
  </blockquote>
  <p>As far as I know, I have not set any redirect URL. Do I need to set this somewhere, or is this the not right approach to get a user to authenticate my page tab?</p>