What is the equivalent Powershell use of Set-AzureADUserExtension in the MS Graph .NET SDK?

[Jonathan Channon (jchannon)]

I have some Powershell that does the below and want to know what the C# is:

Set-AzureADUserExtension -objectid $user.ObjectId -ExtensionName $prop.name -ExtensionValue "foo;bar;delimited;"

I have tried the below which seems to execute but doesn't actually store any data but I'm not even sure its the equivalent.

        var userToUpdate = new User
        {
            AdditionalData = new Dictionary<string, object>
            {
                { extensionName, extensionValue }
            }
        };
        

        await _graphServiceClient.Users[userId]
            .PatchAsync(userToUpdate);