将用户数据（电子邮件+密码）保存到您的应用程序的最佳方法是什么？

I have an application where the user can log in but i don't want the user to enter his credentials every time he wants to use the application. 1 time would be sufficient but how(and whats the best way) to save 2 strings that i can revive by starting the application.I have an application where the user can log in