in src/SigV4RequestSigner.cs [30:40]
public SigV4RequestSigner()
{
ImmutableCredentials awsCredentials = FallbackCredentialsFactory.GetCredentials().GetCredentials();
RegionEndpoint region = FallbackRegionFactory.GetRegionEndpoint();
_access_key = awsCredentials.AccessKey;
_secret_key = awsCredentials.SecretKey;
_token = awsCredentials.Token;
_region = region?.SystemName ?? DefaultRegion; //ex: set via AWS_REGION env variable
_sha256 = SHA256.Create();
}