Application Administrator AD role not providing correct permissions - bash

Question

I'm trying to apply the 'Application Administrator'role to a service principal to allow it to create other service principals in AD. I would have assumed that having the ability to manage all aspects of app registrations etc as explained in the docs here: https://github.com/MicrosoftDocs/azure-docs/blob/master/articles/active-directory/users-groups-roles/directory-assign-admin-roles.md would have allowed me to do this but i still cannot create new service principals in this way?
It looks as if it has created when looking in AD App Registrations but errors out with insufficient privileges
I have tried several approaches through bash & powershell, trying to create the AD application first then creating a service principal from that application id, also tried with the 'Global Admin' role and that works as expected however we're trying to limit as much as possible.
The command i'm trying to run in bash is
az ad sp create-for-rbac -n $spn_name --skip-assignment
And the equivalent in powershell
New-AzAdServicePrincipal -ApplicationId $appid
From an SPN with only the 'Application Administrator' role assigned.
Creating service principal failed for appid 'http://test-spn1'. Trace followed:
{Trace JSON}
Insufficient privileges to complete the operation.

Answer 1

To grant an application the ability to create, edit and delete all aspects of apps (both Application objects and ServicePrincipal objects, represented in the portal under App Registrations and Enterprise Apps, respectively), you should consider the following two app-only permissions (instead of the directory role):
Application.ReadWrite.All - Create Application and ServicePrincipal objects and manage any Application and ServicePrincipal objects.
Application.ReadWrite.OwnedBy - Create Application and ServicePrincipal objects (and automatically get set as owner), and manage Application and ServicePrincipal objects it is owner of (either because it created them, or because it was assigned as an owner).
These permissions are pretty close to what the Application Administrator directory role allows for users. They're available for both Azure AD Graph API (which is the API used by the Azure CLI, the Azure AD PowerShell module (AzureAD), and the Azure PowerShell module (Az)), and Microsoft Graph API (which you should not use for production scenarios, as the application and servicePrincipal entitles are still in beta). The permissions are documented here:
* https://learn.microsoft.com/graph/permissions-reference#application-resource-permissions
Warning: Both of these permissions are very high privilege. By being able to manage Application and ServicePrincipal objects, they can add credentials for those objects (keyCredentials and passwordCredentials) and in doing so, exercise any access which has been granted to those other apps. If an app granted Application.ReadWrite.All is compromised, pretty much all apps are compromised.