It's an interesting problem, and one that's been with us for a very long time. How do I prove to you that I am who I say I am and not an imposter?
It can't be something that I know, because as computing power increases the cost of attempting all possible known things reduces to the point of futility
It can't be something that I possess, because then you're just confirming that I possess something, not that I am someone.
If it's biometric then it had better be capable of detecting when the thing it's measuring has been detached from the owner or we're all in a lot of trouble (and how do you measure fingerprints on someone born with no hands? or the retina prints of someone who's lost their eyes? And DNA is apparently not unique as currently analysed)
Maybe we can do brain scans soon and produce a simple USB hat that measures responses to a displayed image... but that seems like an awful lot of bandwidth for a simple login request.
Maybe we accept that we can't be uniquely identified, and live in a world where we accept a certain amount of fraud as the cost of that. It seems to be the solution so far... so I can go back to having three pretty weak passwords for all my logins and accept the consequence will be that I'll get impersonated sooner or later. I think I can live with that.