swiftでGoogleDriveからファイルをDLしたい

以下のコードで、GoogleDriveからファイルをDLしようとしています。実行すると、"@objc func finishedFileDownload"メソッドの変数errorに Error Domain=com.google.HTTPStatus Code=403 "(null)" と出力されます。

何が間違っているのでしょうか？

swift
1
2import GoogleAPIClientForREST
3import GoogleSignIn
4import UIKit
5import MobileCoreServices
6
7class ViewController: UIViewController, GIDSignInDelegate, GIDSignInUIDelegate, UIImagePickerControllerDelegate, UINavigationControllerDelegate, UITextFieldDelegate {
8    
9    @IBOutlet weak var signInButton: GIDSignInButton!
10    @IBOutlet weak var output: UITextView!
11    @IBOutlet weak var imageView: UIImageView!
12    @IBOutlet weak var textField: UITextField!
13    
14    // If modifying these scopes, delete your previously saved credentials by
15    // resetting the iOS simulator or uninstall the app.
16    // scope: サインイン時の権限
17    private let scopes = [kGTLRAuthScopeDriveFile,kGTLRAuthScopeDrive, kGTLRAuthScopeDriveAppdata, kGTLRAuthScopeDriveMetadata, kGTLRAuthScopeDriveScripts]
18    
19    private let service = GTLRDriveService()
20  
21    override func viewDidLoad() {
22        super.viewDidLoad()
23        // Configure Google Sign-in.
24        GIDSignIn.sharedInstance().delegate = self
25        GIDSignIn.sharedInstance().uiDelegate = self
26        GIDSignIn.sharedInstance().scopes = scopes
27        GIDSignIn.sharedInstance().signInSilently()
28        
29        // Add the sign-in button.
30        view.addSubview(signInButton)
31        
32        // Add a UITextView to display output.
33        output.frame = view.bounds
34        output.isEditable = false
35        output.contentInset = UIEdgeInsets(top: 20, left: 0, bottom: 20, right: 0)
36        output.autoresizingMask = [.flexibleHeight, .flexibleWidth]
37        output.isHidden = true
38        view.addSubview(output);
39    }
40    
41    // サインインした際に呼ばれる
42    func sign(_ signIn: GIDSignIn!, didSignInFor user: GIDGoogleUser!,
43              withError error: Error!) {
44        if let error = error {
45            showAlert(title: "Authentication Error", message: error.localizedDescription)
46            self.service.authorizer = nil
47        } else {
48            self.signInButton.isHidden = true
49            self.output.isHidden = false
50            self.service.authorizer = user.authentication.fetcherAuthorizer()
51        }
52    }
53
54    @objc func finishedFileDownload(fetcher: GTMSessionFetcher, finishedWithData data: NSData, error: NSError?) {
55        
56        if error != nil {
57            //show an alert with the error message or something similar
58            print(error)
59            return
60        }
61        
62        print(data)
63        
64        //do something with data (save it...)
65    }
66   
67    
68    func downloadFile(id: String) {
69        
70        let query = GTLRDriveQuery_FilesGet.query(withFileId: id)
71        
72        service.executeQuery(query, completionHandler: { (ticket, object, error) in
73            print("ticket: (ticket)\n")
74            if error != nil {
75                print(error)
76            }
77       
78            let imageObj = object as! GTLRDrive_File
79       
80            let url = "https://www.googleapis.com/drive/v3/files/(imageObj.identifier!)?alt=media" 
81            
82            // URLを送る
83            let fetcher = GTMSessionFetcher(urlString:url)
84
85            fetcher.beginFetch(withDelegate: self, didFinish: #selector(self.finishedFileDownload(fetcher:finishedWithData:error:)))
86        })
87    }
88}
89
90