title: Header keys become lowercase when interacting with API - React native
body: <p>When interacting with API, the custom Header key always become lowercase. I'm use <code>Fetch</code>, <code>Axios</code>, <code>XMLHttpRequest</code> and <code>Frisbee</code> (javascript network library) but the key always lowercase</p>
  
  <p>My snippet code like this (with <code>fetch()</code> method), The key I'm push is: <strong>'Token-Api'</strong> but the server receive: <strong>'token-api'</strong>, so it's show the error 401. It's work with Postman:</p>
  
  <pre><code> const request = 'https://abcxyz';
   fetch(request, {
     method: 'GET',
     headers: {
       'Content-Type': 'application/json',
       'Token-Api':'...abcxyz....'
     }
   }).then((response) =&gt; {
              log(abcxyz)
          })...
  </code></pre>
  
  <p>What do I need to do?</p>