title: Rails OmniAuth Facebook 'Redirect URL must be absolute'
body: <p>I am trying to set up omniauth to allow users to sign in to my website with facebook. I get the following error when i click on the log in button after following the <a href="https://github.com/plataformatec/devise/wiki/OmniAuth:-Overview" rel="nofollow noreferrer">Github Tutorial</a></p>
  
  <p><a href="https://i.stack.imgur.com/SxhTS.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/SxhTS.png" alt="enter image description here"></a></p>
  
  <p>In my devise.rb file i have:</p>
  
  <pre><code>  config.omniauth :facebook, "*****", "*****",
              callback_url: "CALLBACK_URL"
  </code></pre>
  
  <p>I am using ngrok so i am able to test with a url that isnt localhost. The url generated is <a href="http://46cbf60d.ngrok.io" rel="nofollow noreferrer">http://46cbf60d.ngrok.io</a></p>
  
  <p>In the facebook dashboard settings i have:
  <a href="https://i.stack.imgur.com/I1kXv.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/I1kXv.png" alt="enter image description here"></a>
  <a href="https://i.stack.imgur.com/6NztW.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/6NztW.png" alt="enter image description here"></a></p>
  
  <p>And in the facebook dashboard 'products/facebook login' i have
  <a href="https://i.stack.imgur.com/sZaTR.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/sZaTR.png" alt="enter image description here"></a></p>
  
  <p>Does anybody know how to fix this error?</p>