I am attempting to integrate Zoho with my external webapp. In my webapp a user is intended to log into their Zoho account, then I will store their access/refresh tokens onto my internal user profile and make queries to the Zoho CRM API.

I am currently using this method: https://www.zoho.com/crm/developer/docs/api/v3/scopes.html

My issue is that when a user signs in, Zoho response object does not give me a userId to identify them by. I am given this object:

{
    "access_token": "{access_token}",
    "refresh_token": "{refresh_token}",
    "api_domain": "https://www.zohoapis.com",
    "token_type": "Bearer",
    "expires_in": 3600
}

How do I know which user has entered their information so I know which user to store the refresh token on? Or am I taking an entirely incorrect approach from the start?