Unique nickname (or userId alias)

[Googlom]

It's kind a feature request because I didn't find something what does what I want.
I want a user optionally can set a nickname for himself (like Telegram). Unique, kind an alias to his userid (alicenickname -> usrqwerty1234). So that other users can start chat after finding other by his nickname, as well as mentioning (@alicenickname) in conversations.
I know that it is somekind possible with basic auth (basic:alice tag), but I:

• don't want my nickname be alice123, because someone already sign up with alice and forgot about his account. It's just an example.
• don't use basic auth. I've implemented own custom auth for my usecase.
• think it's not safe to show everyone your login credentials.

Maybe this feature already done? Or give me a direction where to dig, so I can contribute this.