Install the Google.Cloud.Spanner.Admin.Instance.V1 package from NuGet. Add it to
your project in the normal way (for example by right-clicking on the
project in Visual Studio and choosing "Manage NuGet Packages...").
When running on Google Cloud Platform, no action needs to be taken to authenticate.
Otherwise, the simplest way of authenticating your API calls is to
download a service account JSON file then set the GOOGLE_APPLICATION_CREDENTIALS environment variable to refer to it.
The credentials will automatically be used to authenticate. See the Getting Started With
Authentication guide for more details.