title: Underscore (_) not working in headers name Apache 2.4
body: <p>We've using some headers for authentication in our API</p>
  
  <p>Request:</p>
  
  <pre><code>URL: http://lapi.domain.in/test
  
  Header: {AUTH_TOKEN :NUBibTM0QHJkMzM5}
  </code></pre>
  
  <p>But trying to get header AUTH_TOKEN , its return nothing.</p>
  
  <pre><code>$auth_token = $request-&gt;header('AUTH_TOKEN');
  </code></pre>
  
  <blockquote>
    <p>Note: other headers working fine and when its name has been changed
    too AUTH-TOKEN then its working.</p>
  </blockquote>
  
  <p>Apache 2.4, PHP 5.6</p>
  
  <p>Thanks </p>