title: Spring OAuth2 pass state parameter
body: <p>im working on an application which has to support OAuth2 for Account-Linking with Amazon Alexa (Smart home skill).</p>
  
  <p>So i researched the web and started using Spring for that and it works fine, my Android app can easily obtain access_tokens and fetch data.</p>
  
  <p>Now... according to the Amazon Alexa Account-Linking docs the App will pass an "state" parameter which has to be passed to the redirect_uri.
  For more clearity here is the direct link to the documentation: <a href="https://developer.amazon.com/de/docs/account-linking/configure-authorization-code-grant.html#authorization-url-parameters" rel="nofollow noreferrer">https://developer.amazon.com/de/docs/account-linking/configure-authorization-code-grant.html#authorization-url-parameters</a></p>
  
  <p>Anyways i have no clue how to achieve this and i hope someone here can help me here because it starts to drive me crazy</p>