I am looking for a way to re-direct the user back to the page where it came from after a successful log-in.

I would like to use this to allow people to click the "Sign in with Forum account/Facebook/Steam" buttons on our main website (not a part of IPB) and after they successfully signed in I want them to return to the page where they pressed the login button.

Could anyone guide me to the best way of doing this.

Thank you very much.

there is a mod for this

Could you tell me which one?

It must do it by default. No mod needed