Hi, 

I am trying to create a extension for zoho books which sends me webhooks whenever a new invoice is created but once invoice is created and I receive a webhook I want my api to make a few changes into the same invoices and for that I require authentication token of the user, but while installing I don't want my user to do so many things. I want it in a way that a login popup for my app will open once user logs in I setup a organization variable in zoho books(hidden field) and then it should be there whenever I get a webhook but how do I get the authentication token or authorization code for zoho books whenever my app is installed automatically?