Google Drive/OAuth - Can't figure out how to get re-usable GoogleCredentials

Question

I've successfully installed and run the Google Drive Quick Start application called DriveCommandLine. I've also adapted it a little to GET file info for one of the files in my Drive account.

What I would like to do now is save the credentials somehow and re-use them without the user having to visit a web page each time to get an authorization code. I have checked out this page with instructions to Retrieve and Use OAuth 2.0 credentials. In order to use the example class (MyClass), I have modified the line in DriveCommandLine where the Credential object is instantiated:

Credential credential = MyClass.getCredentials(code, "");

This results in the following exception being thrown:

java.lang.NullPointerException
    at com.google.common.base.Preconditions.checkNotNull(Preconditions.java:187)
    at com.google.api.client.json.jackson.JacksonFactory.createJsonParser(JacksonFactory.java:84)
    at com.google.api.client.json.JsonFactory.fromInputStream(JsonFactory.java:247)
    at com.google.api.client.googleapis.auth.oauth2.GoogleClientSecrets.load(GoogleClientSecrets.java:168)
    at googledrive.MyClass.getFlow(MyClass.java:145)
    at googledrive.MyClass.exchangeCode(MyClass.java:166)
    at googledrive.MyClass.getCredentials(MyClass.java:239)
    at googledrive.DriveCommandLine.<init>(DriveCommandLine.java:56)
    at googledrive.DriveCommandLine.main(DriveCommandLine.java:115)

I've been looking at these APIs (Google Drive and OAuth) for 2 days now and have made very little progress. I'd really appreciate some help with the above error and the problem of getting persistent credentials in general.

This whole structure seems unnecessarily complicated to me. Anybody care to explain why I can't just create a simple Credential object by passing in my Google username and password?

Thanks, Brian O Carroll, Dublin, Ireland

* Update *

Ok, I've just gotten around the above error and now I have a new one.

The way I got around the first problem was by modifying MyClass.getFlow(). Instead of creating a GoogleClientServices object from a json file, I have used a different version of GoogleAuthorizationCodeFlow.Builder that allows you to enter the client ID and client secret directly as Strings:

flow = new GoogleAuthorizationCodeFlow.Builder(httpTransport, jsonFactory, "<MY CLIENT ID>", "<MY CLIENT SECRET>", SCOPES).setAccessType("offline").setApprovalPrompt("force").build();

The problem I have now is that I get the following error when I try to use flow (GoogleAuthorizationCodeFlow object) to exchange the authorization code for the Credentials object:

An error occurred: com.google.api.client.auth.oauth2.TokenResponseException: 400 Bad Request
{
  "error" : "invalid_scope"
}
googledrive.MyClass$CodeExchangeException
        at googledrive.MyClass.exchangeCode(MyClass.java:185)
        at googledrive.MyClass.getCredentials(MyClass.java:262)
        at googledrive.DriveCommandLine.<init>(DriveCommandLine.java:56)
        at googledrive.DriveCommandLine.main(DriveCommandLine.java:115)

Is there some other scope I should be using for this? I am currently using the array of scopes provided with MyClass:

private static final List<String> SCOPES = Arrays.asList(
        "https://www.googleapis.com/auth/drive.file",
        "https://www.googleapis.com/auth/userinfo.email",
        "https://www.googleapis.com/auth/userinfo.profile");

Thanks!

Answer 1

I feel your pain. I'm two months in and still getting surprised.

Some of my learnings...

• When you request user permissions, specify "offline=true". This will ("sometimes" sic) return a refreshtoken, which is as good as a password with restricted permissions. You can store this and reuse it at any time (until the user revokes it) to fetch an access token.

• My feeling is that the Google SDKs are more of a hinderence than a help. One by one, I've stopped using them and now call the REST API directly.

• On your last point, you can (just) use the Google clientlogin protocol to access the previous generation of APIs. However this is totally deprecated and will shortly be turned off. OAuth is designed to give fine grained control of authorisation which is intrinsically complex. So although I agree it's complicated, I don't think it's unnecessarily so. We live in a complicated world :-)

Your and mine experiences show that the development community is still in need of a consolidated document and recipes to get this stuff into our rear-view mirrors so we can focus on the task at hand.