// TokenSource returns a JWT TokenSource using the configuration
// in c and the HTTP client from the provided context.
func (c *Config) TokenSource(ctx context.Context) oauth2.TokenSource {
return oauth2.ReuseTokenSource(nil, jwtSource{ctx, c})
}
// ComputeTokenSource returns a token source that fetches access tokens
// from Google Compute Engine (GCE)'s metadata server. It's only valid to use
// this token source if your program is running on a GCE instance.
// If no account is specified, "default" is used.
// Further information about retrieving access tokens from the GCE metadata
// server can be found at https://cloud.google.com/compute/docs/authentication.
func ComputeTokenSource(account string) oauth2.TokenSource {
return oauth2.ReuseTokenSource(nil, computeSource{account: account})
}