title: How to set default HTTP header in Angular2?
body: <p>I know how to set headers for a single HTTP call using the <a href="https://angular.io/docs/ts/latest/api/http/Headers-class.html" rel="noreferrer">Headers class</a>.</p>
  
  <p>Is there a way to do it for <strong>all</strong> HTTP calls? </p>