Can't read principal id from SQL server after it has been created

I'm using Terraform to build and modify my infrastructure in Azure. One problem I have discovered is that when I create or modify an SQL Server it doesn't return a service principal id.

I recently made a bug in the [AzureRM provider for Terraform](https://github.com/hashicorp/terraform-provider-azurerm) as I though the issue was related to their code, but what I have been told is that the API call to _/subscriptions/XXX/resourceGroups/rg-moc-global-weu-test-q7r8/providers/Microsoft.Sql/servers/sql-moc-global-weu-test-q7r8?api-version=2021-02-01-preview_ doesn't return the identity as it is supposed to.

Therefore we concluded that it might be an Azure API issue, and I've been asked to file an issue here for troubleshooting.

You can see the issue [here](https://github.com/hashicorp/terraform-provider-azurerm/issues/20767)

Start with the Azure SQL Servers endpoint and API version in the issue, then compare its create or update response with the behavior reported in the linked Terraform provider issue. Trace whether the service principal identity is absent from the response, and use that comparison to establish the expected API behavior before deciding what specification change is needed.

Written by the indexing model from the issue text.