authorize() should check if cached credentials already exist

[howardbaik]

Currently, authorize() doesn't check if the user already has cached tokens (sometime in the past) and if they do, then don't show these two questions:

I think we should check for tokens in the cache folder and if it doesn't exist, then display the above questions, but if it does exist, then grab those cached tokens.

[cansavvy]

Yes. This has been a thing I keep noticing but have yet to do anything about it. Thanks for tracking it @howardbaek