I dislike loggin in to sites that I have been referred to by other sites in general. Not sure if there is a solution for paypal? Like getting an transaction id

I dislike loggin in to sites that I have been referred to by other sites in general. Not sure if there is a solution for paypal? Like getting an transaction id from a shop, then logging on to PayPal and paying that transaction id? Might be something worthwhile to provide a solution for (possibly even a valid use case for QR codes - pay with phone on a web site)? But then, not many people will care, I suspect :-/