I have a simple HTML form: <form action="https://something.com" method="POST"> <input type="hidden" id="test" value="test"> <input type="submit" value="Send"> </form> I want to write (if it's possible) a javascript that will be executed when a user presses "Send" button add a customer header to the request (before it's send) A couple of notes: I know that I can do this thing in JavaScript () and manipulating a request in it will be trivial. However, for my purposes, the form should be in HTML I know that I can return a header from the backend and it will be send back by the browser. However, again for my purposes, I can't return it by the backend. So, the goal is to capture the request when it will be made and modify it. Is this possible?

Add a custom header to the request in javascript

I have a simple HTML form:

<form action="https://something.com" method="POST">
   <input type="hidden" id="test" value="test">
   <input type="submit" value="Send">
 </form>

I want to write (if it's possible) a javascript that will

A couple of notes:

I know that I can do this thing in JavaScript () and manipulating a request in it will be trivial. However, for my purposes, the form should be in HTML
I know that I can return a header from the backend and it will be send back by the browser. However, again for my purposes, I can't return it by the backend.

So, the goal is to capture the request when it will be made and modify it.

Is this possible?