Steam itself doesn't provide any OAuth 2.0 or something similar to authenticate users with their APIs. You'll need to implement a secure way to authenticate users via Steam.
This isn't a realy OAuth 2.0 method since you won't get any access_token after user sign-in to Steam, what you'll get is users's public Steam ID (number).
That you can use to get public info of that user after successful login.
Steam itself doesn't provide any OAuth 2.0 or something similar to authenticate users with their APIs. You'll need to implement a secure way to authenticate users via Steam. This isn't a realy OAuth 2.0 method since you won't get any access_token after user sign-in to Steam, what you'll get is users's public Steam ID (number). That you can use to get public info of that user after successful login.