How to add JWT to authorization header?

The user above was asking for a BROWSER-BASED means of settings authorization headers, or headers at ALL, for that matter.

(Node.js runs on the server. I realize that the accepted answer above refers to a SERVER authenticating to ANOTHER SERVER, and that the responder calling this "the client side code" is technically correct, with respect to server-to-server communication following the client-server model of who is requesting authorization with whom, but this does not address the true question: how does a browser modify it's authorization header to include a stored token etc.

Aside from the html href, which does not provide a means of accessing or altering headers sent, there are javascript means of sending requests. One can use a standard XHR to demonstrate how one sets the headers via javascript

xhr.open('GET', url, true);
xhr.setRequestHeader("Authorization", "Bearer " + yourtoken);
xhr.send();

Note: There should be a space after the Bearer keyword.

You may be able to find php-templated means of inscribing the token into the rendered page (hidden element?) but javascript running in the browser provides the means for manipulating the request headers. It's worth noting that cookies are automatically sent on all requests for a given domain, while local/session storage requires manually setting them usually.

So, You are pretty much correct with JWT. All you need to do when sending data from client to server (after JWT creation), is to add it to the request header. Many folks will try to keep along the same path as OAuth and add a Bearer token similar to the node snippet below:

var rp = require('request-promise');
options = {
  method: GET,
  uri: 'https://www.example.com/api/sample',
  headers: {
    Authorization: "Bearer <insert_your_JWT_here>"
  }
}
rp(options).then(function(res){
  <handle_response>
}

Granted I know you mentioned PHP, but the workflows are the same, its just the syntax is different.

Now, to verify that this token is present, the server would need to verify() that the token is valid with the secret that was defined. In every request made by the client, for an authorized endpoint, you would need to send this token everytime.