Extend the WP JSON API "Post" Controller to Modify Custom Field Values

json_api_create_post_with_custom_fields.php

// Add to the save() function in post.php
if ( !empty($values["custom"]) ) {
  	foreach ($values["custom"] as $metakey => $metavalue) {
  		update_post_meta($this->id,$metakey,$metavalue);
  	}
}

// create_post example
// http://localhost/site/?json=posts/create_post&dev=1&nonce=xxx&title=Post%20title&status=publish&custom[custom_field_1]=value1&custom[custom_field_2]=value2

// query for listing fields in response
http://localhost/site/?json=posts/create_post&dev=1&nonce=xxx&title=Post%20title&status=publish&custom[custom_field_1]=value1&custom[custom_field_2]=value2&custom_fields=custom_field_1,custom_field_2