What is the best way to perform OAuth2 authentication using akka-http?
<p>Akka HTTP and Spray provide an <code>authenticateOAuth2</code> directive, but <a href="http://doc.akka.io/docs/akka-stream-and-http-experimental/2.0-M1/scala/http/routing-dsl/directives/security-directives/authenticateOAuth2.html" rel="noreferrer">their documentation states</a> that</p>

<blockquote>
  <p>This directive does not implement the complete OAuth2 protocol, but instead enables implementing it, by extracting the needed token from the HTTP headers.</p>
</blockquote>

<p>I also cannot find any libraries that implement OAuth2 for Akka HTTP or Spray.  Is there something I'm missing, or is this simply the state of these libraries right now?</p>