Front end inline editing?

Use the WP JSON REST API in conjunction with jQuery.ajax(). It works pretty well with custom endpoints. Just be sure to use nonces.

<?php
add_action( 'rest_api_init', function () {
    register_rest_route( 'myplugin/v1', '/author/(?P<id>\d+)', array(
        'methods' => 'GET',
        'callback' => 'my_awesome_func',
    ) );
} );