CRM Cards and Multi-Tenant SaaS

[ProVega]

We have a multi-tenant SaaS application and are looking to provide a Card to customers. What is the recommended way of securely adding a Tenant ID to the requests that HubSpot makes to our endpoint?

Current situation:

• User adds the App to their instance
• Card call my app, passing a UserId and UserEmail
  • This UserEmail MIGHT be associated with more than one Tenant in my app;
  • and is it not possible that a use can spoof their email in HubSpot (rare, but possible attack vector)

Ideal is that the callback URL, includes a Tenant / My System ID in a hashed or trusted manner.

Suggestions?