/**
* Auto login to site after GF User Registration Form submission
*/

function we_autologin_gfregistration( $user_id, $config, $entry, $password ) {
    wp_set_auth_cookie( $user_id, false, '' );
    wp_fusion()->auto_login->end_auto_login();
}

add_action( 'gform_user_registered','we_autologin_gfregistration', 10, 4 );