Any possible way to detect user using the PC?

I would like to program something like a chat, but without need to input nickname/false nicknames, so i need a way to automatically detect which player is using PC.

Possible?

No, in the way ComputerCraft works, this is not possible.

If two players peeked into the computer, which player would be the right to choose? - (this is what computercraft would have trouble doing)
The question has also been arised many times, to allow programs to get the players which are accessing the computer, but this has not been a reality…

I hope this answered your question