/// <summary>
 /// Adds the specified Extension to the collection via POST.
 /// </summary>
 /// <param name="extension">The Extension to add.</param>
 /// <param name="cancellationToken">The <see cref="CancellationToken"/> for the request.</param>
 /// <returns>The created Extension.</returns>
 public System.Threading.Tasks.Task <Extension> AddAsync(Extension extension, CancellationToken cancellationToken)
 {
     this.ContentType    = "application/json";
     this.Method         = "POST";
     extension.ODataType = string.Concat("#", StringHelper.ConvertTypeToLowerCamelCase(extension.GetType().FullName));
     return(this.SendAsync <Extension>(extension, cancellationToken));
 }