Following a recent support topic, I noticed that oauth is offered as an authentication method by Zoho.

Zoho gets mentioned in Support on a reasonably regular basis, although not frequently, so without knowing how many users are affected but knowing some are, I suggest we implement use of OAuth with Zoho.

As a business CRM specialist with redirected domain mail, ZOHO probably has some impact in the enterprise/ small business user scope.

Zoho offer instructions for obtaining a secret here. https://www.zoho.com/crm/developer/docs/api/v2/register-client.html