https://blog.canopas.com/golang-interacting-with-google-spreadsheets-b381f819c2eb - spreadsheet-auth

spreadsheet-auth.go

// create api context
ctx := context.Background()

// get bytes from base64 encoded google service accounts key
credBytes, err := b64.StdEncoding.DecodeString(os.Getenv("KEY_JSON_BASE64"))
if err != nil {
	log.Error(err)
	return
}

// authenticate and get configuration
config, err := google.JWTConfigFromJSON(credBytes, "https://www.googleapis.com/auth/spreadsheets")
if err != nil {
	log.Error(err)
	return
}

// create client with config and context
client := config.Client(ctx)

// create new service using client
srv, err := sheets.NewService(ctx, option.WithHTTPClient(client))
if err != nil {
	log.Error(err)
	return
}