Use below code in theme’s functions.php:
add_action(“gform_user_registered”, “autologin”, 10, 4);
function autologin($user_id, $config, $entry, $password) {
wp_set_auth_cookie($user_id, false, ”);
}
Form more info please find this link: http://www.gravityhelp.com/forums/tags/auto-login
AviWeb 