Feature request: Automatic renew

Hi, I've got another idea working with the lib the other day.

What do you think about adding ability to do automatic renew?
The way I see it working would be a method called something like automaticRefresh that would accept config (like normal refresh) plus existing token response (to know expiration) plus a callback that fires on refresh.

I think it's pretty straight forward, let me know what you think ;)

未指定文件或测试。首先检查 React Native bridge 及其 AppAuth refresh flow，然后确定提议的 automaticRefresh 方法如何使用 refresh configuration、现有的 token response 和 refresh callback。Done 应包括自动续期的既定设计和行为。

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