title: Application_PostAuthenticateRequest equivalent in OWIN OAuth
body: <p>To enable my service layer to access the current User Id anytime it needs, I use Thread.CurrentPrincipal.</p>
  
  <p>The service layer is used by two front-end layers, one MVC App and one MVC Web Api used for a Mobile App.</p>
  
  <p>In the web app, I use Forms Authentication and the Principal is set into <code>Application_PostAuthenticateRequest</code>. It works fine.</p>
  
  <p>In the web Api, I use Owin. But I cannot find a way to set that Principal after each request is authenticated with the access token.</p>
  
  <p>I can do it when the user logs in with its credentials by overriding <code>GrantResourceOwnerCredentials</code> into my <code>OAuthAuthorizationServerProvider</code> or when he logs with its refresh token by overriding <code>GrantRefreshToken</code> in the same class.</p>
  
  <p>But where could I assign it for requests automatically authenticated with the access token ?</p>
  
  <p>NB. I know that in my Api Controllers I can access the current User, and it is correctly set, but I don't want to pass it with each call to my service layer.</p>
  
  <p>Thanks.</p>