This namespace is not supported in Azure even today (https://stackoverflow.com/questions/20724861/ad-directory-programming-with-azure-active-directory). That said, why is that information not included explicitly in the official documentation for this namespace?
Suggest to explicitly record the compatibility in Azure for all namespaces, classes, methods in the .NET Framework.

Document Details

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• ID: fd43c5b1-2ae5-247d-6831-0ff500b07096
• Version Independent ID: c7aa119f-d0e4-ab57-7b4e-91b1369ecfbe
• Content: System.DirectoryServices Namespace
• Content Source: xml/ns-System.DirectoryServices.xml
• Product: dotnet-api
• GitHub Login: @dotnet-bot
• Microsoft Alias: dotnetcontent