The main branch can be broken. Make sure to use tagged releases.

For authentication, check out this document.

To use the default client(s), you can try something like:

ctx := context.Background()
client, _ := iam.NewClient(ctx)
defer client.Close()
out, err := client.WhoAmI(ctx, &iam.WhoAmIRequest{})
log.Println(out, err)
...

You can also check the examples here.

The generated gRPC documentation is here.