您可以使用过滤器rest_prepare_user

我想这样的事情应该会奏效。

function my_rest_prepare_user( WP_REST_Response $response, WP_User $user, WP_REST_Request $request ){

    if( in_array( \'administrator\', $user->roles ) ){

        $data = $response->get_data();

        $data[\'custom_field\'] = get_user_meta( $user->ID, \'custom_field\', true );

        $response->set_data( $data );

    }

    return $response;

}
add_filter( \'rest_prepare_user\', \'my_rest_prepare_user\', 10, 3 );

EDIT

function yoursite_update_user( WP_REST_Request $request ){

    $user = get_user_by( \'id\', $request->get_param( \'id\' ) );

    if( $user && in_array( \'administrator\', $user->roles ) ){

        $value = $request->get_param( \'my_field\' );

        update_user_meta( $request->get_param( \'id\' ), \'my_field\', $value );

        return new WP_REST_Response( [
            \'code\'    => \'user_updated\',
            \'message\' =>  \'User Updated\'
        ], 200 );

    } else {

        return new WP_REST_Response( [
            \'code\'    => \'invalid_user\',
            \'message\' =>  \'Invalid user\'
        ], 404 );

    }

}

register_rest_route( \'yoursite/v1\', \'/users/update_my_field/(?P<id>\\d+)\', array(
    \'methods\'             => WP_REST_Server::EDITABLE,
    \'callback\'            => \'yoursite_update_user\',
    \'permission_callback\' => function () {
        return current_user_can( \'edit_users\' );
    },
    \'args\'                => array(
        \'id\' => array(
            \'validate_callback\' => function ( $param, $request, $key ) {
                return is_numeric( $param );
            }
        ),
    ),
) );