Login user after registration

I am looking for a plugin or snippet of code that will auto login the user after they register. I tried https://wordpress.org/plugins/auto-login-after-registration/, http://wordpress.org/plugins/auto-login-user-on-register/
I am already using a plugin that lets the user pick a password at register so the idea is that the user can just enter email, pick a password and be loged in all in one shot. thanks
Do you have any clues on how can I do that?