I found this: https://github.com/Lavoaster/IPS-SteamLoginMethod
Not sure how easy it is to set up though.
IP.Board Apps and Hooks
[REQUEST] New Steam Login
Submitted by Akiko, 10-08-2018, 08:40 AM, Thread ID: 98300
Thread Closed
RE: [REQUEST] New Steam Login 03-09-2018, 03:46 AM #2
03-09-2018, 03:46 AM
#2