add_filter(
   'friends_share_salt',
    function(
        $wp_salt,
        $page_id = null
    ) {
        // Your code here.
        return $wp_salt;
    }
);

apply_filters( 'friends_share_salt', wp_salt( 'nonce' ) )

apply_filters( 'friends_share_salt', wp_salt( 'nonce' ), $page_id )