Stalker uses your boxes mac address (or fake mac address). Your provider has to set this up and assigns your line to your mac address.
Xtream codes use the get.php/player_api.php APIs with username and password.
Most clients offer both for the same domain.
You can get username/password from a mac address with the right software.
But you cannot get mac address from username/password.
If your portal gives you a username or password, then try your domain in a browser.
https://domain.xyz:port/c/
https://domain.xyz:port/stalker_portal/c/
if you get a stalker splash screen, then your client does both.
If so then contact your provider and ask to assign your mac address.
Most people that use multistalker apps and plugins or STB emulators are doing so via hacked stalker lines they have obtain from the internet.