401 Unauthorized adding a user to a datasource

[dkinlnd]

Trying to use the Add Datasource User operation (https://docs.microsoft.com/en-us/rest/api/power-bi/gateways/adddatasourceuser)

I am an owner of the data gateway in question, and I can read the gateway info and datasources fine using the API, but when I try to add a service principal to a datasource I get a 401 error (with no additional detail in the response).

Are there any special permissions required for adding a user to a datasource?

[lbendlin]

The documentation only mentions users and email enabled security groups.  Service principals are not mentioned.

https://docs.microsoft.com/en-us/power-bi/connect-data/service-gateway-data-sources#manage-users