title: Refreshing OAuth token using Retrofit without modifying all calls
body: <p>We are using Retrofit in our Android app, to communicate with an OAuth2 secured server. Everything works great, we use the RequestInterceptor to include the access token with each call.
  However there will be times, when the access token will expire, and the token needs to be refreshed. When the token expires, the next call will return with an Unauthorized HTTP code, so that's easy to monitor.
  We could modify each Retrofit call the following way:
  In the failure callback, check for the error code, if it equals Unauthorized, refresh the OAuth token, then repeat the Retrofit call.
  However, for this, all calls should be modified, which is not an easily maintainable, and good solution.
  Is there a way to do this without modifying all Retrofit calls?</p>