title: Unable to refresh token after expiration
body: <p>I can authenticate and fetch an access_token and the corresponding refresh_token fine (subsequent API interactions are also fine).</p>
  
  <p>However, I seem to only be able to refresh a token (<code>POST</code> to <code>/oauth/token</code> with <code>grant_type=refresh_token</code>) <em>before</em> the <code>access_token</code> actually expires. After the expiration, the same refresh code (exactly that provided within the docs), returns with an error of <code>invalid_grant</code>.</p>
  
  <p>I am using the soundcloud-ruby SDK, FWIW, but I can reproduce it through curl.</p>
  
  <p>As an aside, I found some old messages from the Google Group mentioning that I can request a non-expiring token, but I do not see this mentioned anywhere in the docs. Is this still a viable option?</p>