User registration toggle option

In includes/callback.php we have user registration functionality:

    if ( ! $user_id && email_exists( $user_info->user_email ) == false ) {

        // Does not have an account... Register and then log the user in
        $random_password = wp_generate_password( $length = 12, $include_standard_special_chars = false );
        $user_id         = wp_create_user( $user_info->user_login, $random_password, $user_info->user_email );

For my use case I would like to disable user registration and allow signing in only those users who already exists in website.

Can we have an option in administration panel to toggle user registration on/off?