Assign AppRole to a service principal

I just want to do AppRoleAssignment for a SecureityPrincipal in C# program, for instance, add the permission for "Office 365 Management API" to my web application, but it seems not working. I found a MS document said:

Currently assignment of a service principal to a resource is broken and we’ll work to fix this problem, and update this post when it's fixed.

Is there any fix for this? Or some workaround? 

Thanks!