Unfortunately, it cannot be done in a single call.

If you have the user credentials, you can use its token and just make a single call to /tenants. The returns you the list of project associated with the user token.

If you have the admin token, and only have the user_id: 1. Get all the projects: /tenants 2. Iterate through each project and see if the user has any role in it: /tenants/<project_id>/users/<user_id>/roles