Find all users in my tenant who are invited as guest in another tenant

Hello @GottfriedJocham, I did some lookup and it looks like what you can do here is call the following REST API "https://management.azure.com/tenants?api-version=2020-01-01" and get list of the tenants that a user is a part of (in other words, where the user is added as guest user). One thing to note here is that this API requires a delegated permission (user permission) and how it works is, it would only shows the tenants of the user who has currently logged in and called this API with an access-token that was issued on behalf of that user.

For eg: If User-A logs in to your app that calls this API, then after user-A logs in and then AAD issues an access-token to the app on behalf-of User-A. When the app uses that access-token and calls the api “https://management.azure.com/tenants?api-version=2020-01-01”, then all the tenants that User-A is part of (added as guest user) would get listed.

To read more on this API, please refer: https://docs.microsoft.com/en-us/rest/api/resources/tenants/list