How do I use WebAppsOperationsExtensions in Azure C# SDK

Question

This is the method I'm trying to use
WebAppsOperationsExtensions.BackupAsync(IWebAppsOperations, String, String, BackupRequestInner, CancellationToken)

However, I don't know how to get IWebAppsOperations object, as the Microsoft implementation is not public.

Documentation is not helpful:

https://learn.microsoft.com/en-us/dotnet/api/microsoft.azure.management.appservice.fluent.webappsoperationsextensions.backupasync?view=azure-dotnet#Microsoft_Azure_Management_AppService_Fluent_WebAppsOperationsExtensions_BackupAsync_Microsoft_Azure_Management_AppService_Fluent_IWebAppsOperations_System_String_System_String_Microsoft_Azure_Management_AppService_Fluent_Models_BackupRequestInner_System_Threading_CancellationToken_