I have two use cases for APIs that I don't understand how to authenticate.

1) I want to make myself a desktop timer app. I don't want to have to run a server to redirect to. I also don't want to have to open the Self Client page every time. I just want an API key so that I can connect to the APIs as myself.

2) I may want to make my webapp know how much the user owes me. I can map the user to a Customer in Books. I want to authenticate as myself, not the person logged into the webapp.

However https://www.zoho.com/books/api/v3/#oauth doesn't explain how to do this. Please explain. Thanks.