Prefer provided credentials if they are present in FirestoreOptions

[andrewparmet]

Addresses #3458.

As of 0.52.0-beta, calls to setCredentials() on FirestoreOptions are effectively ignored. This is because GrpcTransportOptions.setUpCredentialsProvider() is no longer called in GrpcFirestoreRpc - instead the settings builder just pulls the credentials provider regardless of whether or not a fixed credential was supplied in the original options.

It used to be:

settingsBuilder.setCredentialsProvider(
    GrpcTransportOptions.setUpCredentialsProvider(options));

Today it reads:

settingsBuilder.setCredentialsProvider(options.getCredentialsProvider());

This was changed in #3320. (Diff line)

The call can be restored in the same class with some conditional logic, or the FirestoreOptions can try to return the correct CredentialsProvider.

[pongad]

@schmidt-sebastian Can you take a look?

[schmidt-sebastian]

Thanks for sending this over! The problem you described exists in both the CredentialsProvider and the ChannelProvider. I have opened a PR to deal with both: #3472

Let's leave this open until 3472 is approved.