Open a webpage, login via POST and come back somehow in a Cordova app

I had a specific question here, but since there does not seem to be an easy way to solve it I would like to ask the more general problem here.

In a Cordova app I want to open a webpage, where I should login via a POST request (that sets a cookie). The user should be able to browse the page and be able to return to the app somehow.

My first try was an iFrame, but the X-Frame-Option SAME-Origin prohibited display. My second try was using InAppBrowser, but I cannot get the injected POST request to work.

So what would you suggest? If there is any possible way that does not require a change on the external webpage I would prefer that, but as a last resource I'd also use that.