Custom post metadata not appearing in public API

Question

I'm using wordpress.com's public REST API to retrieve custom posts from a Wordpress installation. The JSON that's being returned is missing all the custom fields, however. The fields are definitely there and working, because I can filter on them. For example this URL:

https://public-api.wordpress.com/rest/v1/sites/swnfest.com/posts/?type=artist&meta_key=facebook&meta_value=outfitoutfitoutfit

is successfully limiting based on the facebook custom field, but that field isn't present in the response. Judging by the criteria for including custom fields in this article:

If the user performing the request is unauthenicated, he or she will not be able to add, edit or delete any metadata; will be able to read any metadata for which the key doesn’t begin with _ but will not be able to read any metadata which begins with _ unless it is whitelisted.

the field should be appearing. Is there something I'm missing, or is this a bug?

Answer 1

Try using the rest_api_allowed_public_metadata filter to whitelist the facebook custom field. It will then appear in the response:

add_filter( 'rest_api_allowed_public_metadata', 'jeherve_allow_fb_metadata' );
function jeherve_allow_fb_metadata() {
    // only run for REST API requests
    if ( ! defined( 'REST_API_REQUEST' ) || ! REST_API_REQUEST )
        return $allowed_meta_keys;

    $allowed_meta_keys[] = 'facebook';

    return $allowed_meta_keys;
}