Zoho Books Customer Portal API

Zoho Books Customer Portal API

We have successfully created a customers synchronization between the OpenCart ecommerce software and Zoho Books, with the aid of the RESTful Zoho Books API. As a next step, is there a way to create a 'Login with Zoho', similar to 'Login with Google' or 'Login with Facebook' for our ecommerce site?

I asked Zoho Books support, they were useless. They said there is no Customer Portal API, but that one of their Partners could help. However, no further leads or details. It's strange that Zoho can't implement this, but their Partners can?  Hence my posting here. Maybe someone has a solution for this?

J.N.