NFC phone's UID as a Login Account

[G2345]

Hi,
I'm working on a project. The basic Idea is I want to use NFC phone's UID as an unique identifier for log in process. User will be provided a client, where they only need to tap Log in and it will read the NFC UID from the phone, send it to the server, if it's registered then the log in process is successful. But I'm totally new to the technology so I want to ask if doing so is really possible? I've been researching for awhile and found some articles say that the UID is randomly generated each time it's scanned. Is that true? Is there any real fixed UID that can be used to serve my purpose? Please help me, thanks!

[oniongarlic]

I did some quick testing with reading UID of a BB10DevAlpha from a N9. Indeed, the UID changes every time.

[G2345]

I did some quick testing with reading UID of a BB10DevAlpha from a N9. Indeed, the UID changes every time.

Thank you for your answer.
So basically, there's no fixed value that can be used to uniquely identify user using their phone only? Oh and is it the same for NFC Tag? I mean does its UID change each time it's scanned too?