window.open with headers

Can I control the HTTP headers sent by window.open (cross browser)?

No

If not, can I somehow window.open a page that then issues my request with custom headers inside its popped-up window?

• You can request a URL that triggers a server side program which makes the request with arbitrary headers and then returns the response
• You can run JavaScript (probably saying goodbye to Progressive Enhancement) that uses XHR to make the request with arbitrary headers (assuming the URL fits within the Same Origin Policy) and then process the result in JS.

I need some cunning hacks...

It might help if you described the problem instead of asking if possible solutions would work.

If you are in control of server side, it might be possible to set header value in query string and send it like that? That way you could parse it from query string if it's not found in the headers.

Just an idea... And you asked for a cunning hack :)

Sadly you can't control headers when doing window.open()

Nice and easy, how I managed to open a file with custom headers:

const viewFile = async (url) => {

  // Change this to use your HTTP client
      fetch(url, {/*YOUR CUSTOM HEADER*/} ) // FETCH BLOB FROM IT
        .then((response) => response.blob())
        .then((blob) => { // RETRIEVE THE BLOB AND CREATE LOCAL URL
          var _url = window.URL.createObjectURL(blob);
          window.open(_url, "_blank").focus(); // window.open + focus
      }).catch((err) => {
        console.log(err);
      });
};

• Download file to cache
• window.open to cache