Is there a way to detect wht subdomain someone uses to access server?

Not sure if this is the right place to ask, but maybe someone here knows.

I am trying to set up a referral system which will allow someone to set up a portal on their server to direct people to a custom domain that points to my server. So instead of mc.MyServer.com, it would be referralname.MyServer.com. But I am not sure if it's even possible to detect what sub domain people are logging in with, and if so, is bungee capable of recording that somehow, are there any plugins around here capable...

Is there a way to detect wht subdomain someone uses to access server?