Paid
If you are self-hosting Cal.com and have implemented 3rd party integrations on your platform, you can now use those integrations on your Cal.com instance.
This only works if you have integrated Cal.com into your platform. Users must consent to give access to your platform, and you are simply using Cal.com's code within your platform.
At a high level, users will add the app on your platform. When the credentials are made, you will hit a webhook on your instance of Cal.com to add those credentials to your Cal.com database. When your instance of Cal.com uses that app and the credentials are expired, it will then make a request to your platform for new credentials.
Here's a guide to help you make use of this feature.