Is it possible to set up an own push service within an intranet?

Question

I would have asked this in a follow-up comment to this comment but my reputation is still too low.
So here are the questions: Is it possible to change the endpoint URL of a browser or to add an endpoint URL so that my application can send its POST request not to a web service owned by the browser manufacturer but to a web service that runs inside my intranet? As my application is run in an intranet without connection to the internet a customized browser wouldn't be a perfect solution but it would be possible.
And now for the 2nd part: If it is possible - are there ready-to-use push service libraries for PHP? So far all I've found are libraries that let an application send notifications like https://github.com/web-push-libs/web-push-php.

Answer 1

Is it possible to change the endpoint URL of a browser

No, currently it is not possible to change the browser push service.

And in any case you would also have to run an instance of the browser push service on your own servers (e.g. https://github.com/mozilla-services/autopush).