Java: Google AppEngine: OAuth: Google Drive API 访问用户的 Google Drive 内容由 ZC6E190B28404633333333333

Question

Scenario: I am working on a Web Application on Google AppEngine where users have to access files from their own Google Drive. I have looked for online help and this is what I have figured out.

I have used this link for help that worked fine while testing with local machine https://github.com/gsuitedevs/java-samples/blob/master/drive/quickstart/src/main/java/DriveQuickstart.java

Step 1 (Seemed simple): Enable Google Drive API and Setup necessary credential, ie OAuth 2.0 Client ID for Web Application. (This is done while enabling IAP on Google AppEngine, so I did not do it again. Whenever anyone opens the web application, he/she is asked to authenticate via iap.googleapis.com and details saved. This works fine). Also, I have added Google Drive Scopes to the OAuth consent screen (../auth/drive.appdata &../auth/drive.file) that don't need verification by Google.

Step 2 : Downloaded the credentials.json from OAuth Client ID and stored inside "resources" folder created in the root of application package (inside main folder, next to java and webapp folders)

Step 3 : I have created a testing class (GoogleDriveServiceTest.class) that includes following code:

String USER_ID1 = UserServiceFactory.getUserService().getCurrentUser().getUserId();
List<String> SCOPES = Collections.singletonList(DriveScopes.DRIVE_METADATA_READONLY);
NetHttpTransport httpTransport = new NetHttpTransport();
JsonFactory jsonFactory = new JacksonFactory();
InputStream inputStream = 
       GoogleDriveServiceTest.class.getResourceAsStream("/credentials.json");
if (inputStream == null) 
    throw new FileNotFoundException("Required credentials file not found");
GoogleClientSecrets googleClientSecrets = 
            GoogleClientSecrets.load(jsonFactory, new InputStreamReader(inputStream));
    
AppEngineDataStoreFactory appEngineDataStoreFactory = 
                              AppEngineDataStoreFactory.getDefaultInstance();

//IS SOMETHING MISSING HERE???
    
GoogleAuthorizationCodeFlow flow = new GoogleAuthorizationCodeFlow
                    .Builder(httpTransport, jsonFactory, googleClientSecrets, SCOPES)
                    .setDataStoreFactory(appEngineDataStoreFactory)
                    .setAccessType("offline")
                    .build();

Now I am trying to create the credential to be used for accessing Google Drive with this line:

Credential credential = flow.loadCredential(USER_ID1);

that is returning null.

In my opinion I am missing to assign the credentials to AppEngineDataStoreFactory based on what I have seen in the example from the github link above. However, I am not sure if this is the issue, and if it is, how do I resolve it.

Is there a straight forward way to assign credentials using logged in userID obtained from UserServiceFactory.getUserService().getCurrentUser().getUserId()? Or should I be obtaining accetoken and create the credential? if so, how?

(I don't want to use javascript as the same does not seem suitable for web application)

Any help would be great!!!!

PS: I also wanted to add a point that user needs to access only files added by the same web application either via web or from android

Update #1 responding to @Aerials: Here is the code I was trying with to get the TokenResponse:

VerificationCodeReceiver receiver = new GooglePromptReceiver();
(I know above one is not the right option, but I am not able to find any other)    
AuthorizationCodeRequestUrl authorizationUrl =                          
        flow.newAuthorizationUrl().setRedirectUri(receiver.getRedirectUri());
String code = receiver.waitForCode();
(Above line returns: java.util.NoSuchElementException: No line found)
TokenResponse tokenResponse = 
            flow.newTokenRequest(code).setRedirectUri(redirectUri).execute();

Update #2 Code that worked in getting the TokenResponse and rest of the tasks of creating a Credential and connect to Google Drive successfully:

GenericUrl genericUrl = new GenericUrl(request.getRequestURL().toString());
genericUrl.setRawPath("/googleDriveTest");
String redirectUri = genericUrl.build();

(redirectUri should match with authorised redirect URI inside OAuth ClientID under GCP API Credentials. If you added it now, you need to redownload the credentials.json file)

String redirectUrl =  authorizationCodeFlow
                            .newAuthorizationUrl()
                            .setRedirectUri(redirectUri)
                            .build();
String authorizationCode = request.getParameter("code");
if (authorizationCode == null || authorizationCode.isEmpty())
              response.sendRedirect(redirectUrl);
TokenResponse tokenResponse = authorizationCodeFlow
                                    .newTokenRequest(authorizationCode)
                                    .setRedirectUri(redirectUri).execute();
authorizationCodeFlow.createAndStoreCredential(tokenResponse, USER_ID1);
Credential credential = authorizationCodeFlow.loadCredential(USER_ID1);
Drive service = new Drive.Builder(httpTransport, jsonFactory, credential)
                         .setApplicationName("myapplicationname")
                         .build();

Answer 1

You need to first create and store the credentials in the flow's credential store:

createAndStoreCredential(TokenResponse response, String userId)

to be able to load them with loadCredential(String userId)

The loadCredential() method will return credential found in the credential store of the given user ID or null for none found.