title: How to specify Authorization Header for a source in mapbox-gl-js?
body: <p>How do I set a request header for a wms source with mapbox-gl-js?  I need all tile requests to add a header that looks like:</p>
  
  <pre><code>Authorization: "Bearer base64-encoded-token"
  </code></pre>
  
  <p>The <a href="https://www.mapbox.com/mapbox-gl-js/example/wms/" rel="noreferrer">WMS example</a>, <a href="https://www.mapbox.com/mapbox-gl-js/api/#Map#addSource" rel="noreferrer">map#addSource</a> and <a href="https://www.mapbox.com/mapbox-gl-js/api/#Map#addLayer" rel="noreferrer">map#addLayer</a> lead me to believe it is not possible to set tile request headers.</p>