title: Tomcat realm for oauth2?
body: <p>I want to use tomcat's realm mechanism for authorization, but I want to allow users to either login directly (say <code>JDBCRealm</code>) or login via OAuth2 (say through LinkedIn). I found out that in principle, one could use <code>CombinedRealm</code> to combine two different methods of authentication, but I cannot find anything about any realm implementation for OAuth2. </p>
  
  <p>PS: I am also open to completely different way to allow the dual authentication requirement.</p>