panel.html

<!DOCTYPE html>
<html>
    <head>
        <script src="https://extension-files.twitch.tv/helper/v1/twitch-ext.min.js"></script>
    </head>
    <body>
        <script type="text/javascript">
          var token = "";
          
          var twitch = window.Twitch.ext;

          twitch.onAuthorized(function(auth) {
            token = auth.token; 
            twitch.rig.log("onAuthorized() fired, received JWT: " + token)
          });

          twitch.listen('broadcast', function(topic, contentType, message) {
            twitch.rig.log("listen() fired, received PubSub message: " + message)
          });

          function ping() {
            twitch.rig.log("button clicked, pinging https://localhost:8081/api/ping")
            fetch('https://localhost:8081/api/ping', {
              method: 'get', 
              headers: new Headers({
                'Authorization': 'Bearer ' + token,
              })
            })
          }
        
        </script>    
        <button onclick="ping()">
            Ping
        </button>
    </body>
</html>