Google Drive - View Controller - Authorizer

GoogleDriveViewController_Authorizer.swift

import GTMSessionFetcher

extension ViewController: GIDSignInDelegate, GIDSignInUIDelegate {
    func sign(_ signIn: GIDSignIn!, didSignInFor user: GIDGoogleUser!, withError error: Error!) {
        // A nil error indicates a successful login
        if error == nil {
            // Use the authenticated user's credentials when querying the Google Drive API.
            self.googleDriveService.authorizer = user.authentication.fetcherAuthorizer()
        } else {
            self.googleDriveService.authorizer = nil
        }
        
        googleSignInButton.isHidden = error == nil
    }
}