GoogleCredential.getApplicationDefault().getAccessToken() == NULL on GCP about google-auth-library-java

[chingor13]

I suggest we do (1) and (2).

We should encourage people who are explicitly trying to access the AccessToken to do something like:

GoogleCredentials credentials = GoogleCredentials.getApplicationDefault();
AccessToken token = credentials.refreshAccessToken();
// OR
credentials.refresh();
AccessToken token = credentials.getAccessToken();

For (3), there are a few issues:

• OAuth2Credentials#getAccessToken() would need to either add throws IOException or try to refresh and then silently swallow any exceptions.
• For any swallowed exception, you will miss out on the contents of the exception and not realize that we are potentially making extra auth requests
• Anyone who is currently using getAccessToken() does not expect to be making IO calls. This is a behavior change and will break downstream users.

[chingor13]

Adding a refreshIfExpired() that smartly refreshes a possibly expired token would make the way to do this:

GoogleCredentials credentials = GoogleCredentials.getApplicationDefault();
credentials.refreshIfExpired();
AccessToken token = credentials.getAccessToken();

This should be easier to reason about then calling credentials.getRequestMetadata(uri) which is what the client libraries call before each request (which will load or refresh the credentials if necessary).

[chingor13]

Next release will contain this method and updated documentation.