WP-API custom auth

function checkApiAuth( $result ){
    
    // if user and token from app match user meta in wp, continue
    
    $app_token = $_GET['app_token'];
    
    $user_id = $check_user_id;
    
    $wp_token = get_user_meta( $user_id, 'app_token', true);
 
    if( empty( $app_token ) )
        $result = false;
        
    if( $wp_token === $app_token )
        $result = true;
 
    return $result;
            
}
add_filter('json_authentication_errors', 'checkApiAuth');