Question about PoE API

I'm a new developer so sorry if i'm asking random things, but i wanna know if there is any way, not being like from stash tabs, to get the character name from someone, basically what i wanna do is a form to the player register (or anything like that) and then i get their ingame username, to show up on a list, to other players to contact, just like poe.trade, but it's not related to trade, so the public stash API would not really be the greatest.

You can use the officially documented API, and we have also had a GGG employee say that they are "OK" with using the API that the website character display stuff uses.

Beyond that, which may provide the features you need, there isn't much you can do.

poe tool developers do post on their own forums on reddit

https://www.reddit.com/r/pathofexiledev/

you will get more answers there (if there any)