401 when authenticating through a service account and OAuth2 on GoogleDrive

Question

I seem to have hit a wall while trying to get a Java application to list the files stored in my GoogleDrive folder.

I have a project setup in the developer console. I enabled the Drive API for this project. I created Auth credentials for the service account - and use the received key P12.

My code is as follows:

import com.google.api.client.auth.oauth2.Credential; import com.google.api.client.auth.oauth2.CredentialRefreshListener; import com.google.api.client.auth.oauth2.TokenErrorResponse; import com.google.api.client.auth.oauth2.TokenResponse; import com.google.api.client.googleapis.auth.oauth2.GoogleCredential; import com.google.api.client.http.HttpTransport; import com.google.api.client.http.javanet.NetHttpTransport; import com.google.api.client.json.JsonFactory; import com.google.api.client.json.jackson2.JacksonFactory; import com.google.api.services.drive.Drive; import com.google.api.services.drive.DriveScopes; import com.google.api.services.drive.model.File; import com.google.api.services.drive.model.FileList; import java.io.IOException; import java.security.GeneralSecurityException; import java.util.Collections; import java.util.List; public class GoogleDriveTest { /** Global instance of the JSON factory. */ private static final JsonFactory JSON_FACTORY = new JacksonFactory() ; /** instance of the HTTP transport. */ private static final HttpTransport HTTP_TRANSPORT = new NetHttpTransport() ; /** Global instance of the Google Drive - the first connect will initialize */ private static Drive drive; /* * instance variables */ private String accessToken ; public static void main(String[] args) throws GeneralSecurityException, IOException { String CLIENTID = " [e-mail] count.com" ; String CLIENTUSER = " [e-mail] " ; String P2FILE = "random/src/main/resources/test.p12" ; try { GoogleCredential credential = new GoogleCredential.Builder().setTransport(HTTP_TRANSPORT) .setJsonFactory(JSON_FACTORY) .setServiceAccountId(CLIENTID) .setServiceAccountScopes(Collections.singleton(DriveScopes.DRIVE_FILE)) .setServiceAccountPrivateKeyFromP12File(new java.io.File(P2FILE)) .setServiceAccountUser(CLIENTUSER) .addRefreshListener(new CredentialRefreshListener() { @Override public void onTokenResponse( Credential credential, TokenResponse tokenResponse) throws IOException { String token = tokenResponse.getAccessToken(); System.out.println("GOOGLEDRIVE token refreshed " + tokenResponse.getTokenType() + " successfully"); } @Override public void onTokenErrorResponse( Credential credential, TokenErrorResponse tokenErrorResponse) throws IOException { System.out.println("GOOGLEDRIVE token refresh failure : " + tokenErrorResponse); } }) .build(); /* * set up the global Drive instance */ drive = new Drive.Builder(HTTP_TRANSPORT, JSON_FACTORY, credential).setApplicationName("API Project").build(); /* * output results */ Drive.Files.List fileRequest = drive.files().list() ; FileList afiles = fileRequest.execute() ; List<File> bFiles = afiles.getItems() ; for(File file : bFiles) { System.out.println(file.getTitle()) ; } } catch (GeneralSecurityException | IOException e) { e.printStackTrace(); } } } 

But the conclusion I see is this:

 GOOGLEDRIVE token refresh failure : null com.google.api.client.auth.oauth2.TokenResponseException: 401 Unauthorized at com.google.api.client.auth.oauth2.TokenResponseException.from(TokenResponseException.java:105) at com.google.api.client.auth.oauth2.TokenRequest.executeUnparsed(TokenRequest.java:287) at com.google.api.client.auth.oauth2.TokenRequest.execute(TokenRequest.java:307) at com.google.api.client.googleapis.auth.oauth2.GoogleCredential.executeRefreshToken(GoogleCredential.java:384) at com.google.api.client.auth.oauth2.Credential.refreshToken(Credential.java:489) at com.google.api.client.auth.oauth2.Credential.intercept(Credential.java:217) at com.google.api.client.http.HttpRequest.execute(HttpRequest.java:859) at com.google.api.client.googleapis.services.AbstractGoogleClientRequest.executeUnparsed(AbstractGoogleClientRequest.java:419) at com.google.api.client.googleapis.services.AbstractGoogleClientRequest.executeUnparsed(AbstractGoogleClientRequest.java:352) at com.google.api.client.googleapis.services.AbstractGoogleClientRequest.execute(AbstractGoogleClientRequest.java:469) at GoogleDriveTest.main(GoogleDriveTest.java:81) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) at java.lang.reflect.Method.invoke(Method.java:483) at com.intellij.rt.execution.application.AppMain.main(AppMain.java:134) Process finished with exit code 0 

Can someone point out some pointers to access the service account on Google Drive and what can I do wrong here?

Since the service account was created in my Google account ( [e-mail] ), I assumed that it would have access to Drive after activating the API.

I saw other messages about granting access to service accounts in a domain account through the admin console, but my account is a regular / standard google account. I'm not even sure what a domain account is!

All help would be greatly appreciated.