title: Devise with omniauth-facebook "Invalid Credentials"
body: <p>I'm trying to get Facebook authentication working with Devise through omniauth-facebook, I've followed the instructions here: <a href="https://github.com/plataformatec/devise/wiki/OmniAuth%3a-Overview" rel="noreferrer">https://github.com/plataformatec/devise/wiki/OmniAuth%3a-Overview</a></p>
  
  <p>When I follow the login with Facebook link I am redirected to Facebook to login and accept the requested permissions. </p>
  
  <p>I am then taken back to /users/sign_in with the error message "Could not authorize you from Facebook because "Invalid credentials""</p>
  
  <p>Looking at the server logs the redirect comes from "/users/auth/facebook/callback?code=[long text string]" which is being processed with Users::OmniauthCallbacksController#failure rather than Users::OmniauthCallbacksController#facebook as I would have expected if it had worked. </p>
  
  <p>Any suggestions as to why this is happening and how to resolve it much appreciated.</p>