how to retrieve user via rest api using custom meta and/or email

I managed to solve my issue by taking a look at \WP_REST_Users_Controller::get_items and noticing that there’s not an automatic way to filter via meta terms. Instead you need to apply_filters to actually input the args in the array.

So in order to achieve my searching I had to do these things.

1. in functions.php or a plugin

     foreach ($fields as $field) {
        //register meta field
        register_meta('user', $field, [
            'single' => true,
            'show_in_rest' => true,
            'type' => 'string',
        ]);
    
        //register search function in rest api
        add_filter('rest_user_query', function ($args, $request) use ($field) {
            if (isset($request[$field]) && !empty($request[$field])) {
                $args['meta_query'][] = [
                    'relation' => 'AND',
                    [
                        'key' => $field,
                        'value' => $request[$field],
                        'compare' => '='
                    ]
                ];
    
            }
            return $args;
        }, 10, 2);
    }

2. In the rest request just add the params

    [
        'trdr' => $trdr
    ]

Email can be searched like this

        [
            'search' => $email,
            'search_columns' => ['user_email']
        ]