title: External authentication on nginx reverse proxy level
body: <p>We have PHP application in Laravel, that does login/pass authentication for us. Then 
  inside this application, we have XX external links to our VPS. 
  On VPS we use nginx as reverse proxy to apache handling the backend.
  Currently everyone that has a link to external VPS can access the content. We would like to limit access to users that have logged in to our main app (Laravel, PHP).</p>
  
  <p>We would like to send something like a token when user clicks a link on our main Laravel PHP app, that gets verified on nginx proxy, without user needing to supply any credentials (since he was once authenticated on Laravel PHP app).</p>
  
  <p>To sum up:</p>
  
  <pre><code>Laravel PHP Application that auths user.
  User clicks external link.
  Gets authenticated on nginx reverse proxy.
  Based on result of auth either gets the content or gets denied.
  </code></pre>
  
  <p>Our interest is in nginx server: 
  <strong>How can we authenticate users on nginx reverse proxy level without needing user to supply any credentials manually, access it just by clicking on link on our main app?</strong></p>