https://wordpress.org/plugins/wp-favorite-posts-extended/

Based on plugin “WP Favorite Posts”,added json api feature.

This plugin is based on “WP Favorite Posts”,and extends json api to provide access for mobile apps. Three methods are provided: wpfp/add postid: required cookie: optional wpfp/remove postid：required cookie：optional wpfp/lists cookie ：optional The cookie param is the same as “JSON API USER” plugin used.

These methods support users not logged,if the client side can receive and send cookies.

code can be found at: https://github.com/avrilmaomao/wp-favorite-posts-extended