How to add extension to user

gistfile1.txt

OpenTypeExtension newExtension = new OpenTypeExtension();
newExtension.ExtensionName = "com.contoso.trackingKey";

newExtension.AdditionalData = new Dictionary<string, object>();
newExtension.AdditionalData.Add("trackingKeyMajor", "ABC");
newExtension.AdditionalData.Add("trackingKeyMinor", "123");

var extension = await graphClient.Users[email].Extensions.Request().AddAsync(newExtension);