OAuth2 vs Session Authentication I'm setting up a OAuth2 Server using the OAuth2 Server module.  Everything tests out as expected.  I login, get the authentication code, which I then trade in for an access_token, which tests out successfully.

The issue comes when requesting a resource that's handled by the services module.  It looks like it's starting a session for the anonymous user instead of calling the other authentication hooks.

After all, if one authentication method fails, it shouldn't assume that it's the only authentication method possible.

Any ideas on how to use OAuth2 authentication code authorization to access services endpoints?

Here's the snip from services.runtime.inc line 116 where it's only looking for one authentication module, it seems.  

foreach ($endpoint-&gt;authentication as $auth_module =&gt; $settings) {
  if (isset($settings) &amp;&amp; $auth_error = services_auth_invoke($auth_module, 'authenticate_call', $settings, $controller, $args)) {
    return services_error($auth_error, 401);
  }
}
Make sure the selected authentication methods are enabled for the server, e.g:

admin/structure/services/list/rest_api