Create Get-TenantIdFromSubscriptionId.ps1

For future use

Author: rvdwegen

Modules/CIPPCore/Public/Get-TenantIdFromSubscriptionId.ps1

@@ -0,0 +1,26 @@
+function Get-TenantIdFromSubscriptionId {
+    param (
+        [Parameter(Mandatory = $true)]
+        [string]$SubscriptionId
+    )
+
+    # Full credit goes to Jos Lieben
+    # https://www.lieben.nu/liebensraum/2020/08/get-tenant-id-using-azure-subscription-id/
+    
+    try {
+        Invoke-WebRequest -UseBasicParsing -Uri "https://management.azure.com/subscriptions/$($SubscriptionId)`?api-version=2015-01-01" -ErrorAction Stop
+    } catch {
+        # The error response contains the WWW-Authenticate header with the tenant ID
+        $response = $_.Exception.Response
+    }
+    
+    # Extract tenant ID from WWW-Authenticate header
+    $authHeader = $response.Headers.GetValues("WWW-Authenticate")[0]
+    
+    # Use regex to extract the tenant ID
+    if ($authHeader -match "login\.windows\.net\/([0-9a-fA-F]{8}-([0-9a-fA-F]{4}-){3}[0-9a-fA-F]{12})") {
+        return $matches[1]
+    }
+    
+    return $null
+}