title: how to access header in lumen routing file(web.php)
body: <p>how to access header in routing file lumen ?</p>
  
  <p>i want to use header parameters values as namespace in route group in web.php.</p>
  
  <p>example :</p>
  
  <pre><code>$router-&gt;group(['namespace' =&gt; 'Request::header('version')'], function() use ($router) 
  {
      $router-&gt;post('login', 'UserController@loginUser');
      $router-&gt;post('test', 'UserController@testApi');
  });
  </code></pre>
  
  <p>if request header version param v1 then it use v1 namespace,if v2 then use v2 namespace.something like versioning. </p>