title: OAuth callback URL parameters with Doorkeeper
body: <p>I'm Using OAuth2 with Doorkeeper to protect my API.</p>
  
  <p>The problem is that one client had several different flows in which he redirects users to my OAuth flow.</p>
  
  <p>He would like to <strong>dynamically add some parameters</strong> when redirecting the user to my OAuth flow and <strong>get these parameters back</strong> when I'm calling his callback URL. This way he will be able to tell from which flow this callback originated.</p>
  
  <p>Is this possible with OAuth 2? with Doorkeeper? How?</p>
  
  <p><strong>Edit:</strong></p>
  
  <p>Thanks Zólyomi István for your hint.
  I set the state parameter before calling the auth endpoint and got it back in the callback. However, I found that I get back a state parameter with some apparently random string even if I don't set anything. Any idea what it is? I'd like to be sure I'm not messing up anything...</p>