title: Dealing with Oauth 2.0-facebook gem error 100: This authorization code has been used
body: <p>I have been working on setting up facebook authentication for my rails app and while testing, after logging-in with my facebook account, I keep getting this error:</p>
  
  <pre><code>OAuth2::Error:
  {"error":{"message":"This authorization code has been used.","type":"OAuthException","code":100}}
  </code></pre>
  
  <p>I'm not really sure where to begin with this, but can't seem to find anything else online about it.  Any guidance would be appreciated, happy to provide more info if it would be useful.</p>