Issue 351: Reimplement OAuth2 - Step 2 (Auth PCL - only data types)

Src/GoogleApis.Auth/JsonWebToken.cs

 /*
 Copyright 2013 Google Inc
 
 Licensed under the Apache License, Version 2.0 (the "License");
 you may not use this file except in compliance with the License.
 You may obtain a copy of the License at
 
 http://www.apache.org/licenses/LICENSE-2.0
 
 Unless required by applicable law or agreed to in writing, software
@@ skipping 84 matching lines @@
 public string JwtId { get; set; }
 
 /// <summary>
 /// Gets or sets type claim that is used to declare a type for the c
ontents of this JWT Claims Set or·
 /// <c>null</c>.
 /// </summary>
 [Newtonsoft.Json.JsonPropertyAttribute("typ")]
 public string Type { get; set; }
 
 /// <summary>Gets the audience property as a list.</summary>
+[Newtonsoft.Json.JsonIgnoreAttribute]
 public IEnumerable<string> AudienceAsList
 {
 get
 {
 var asList = Audience as List<string>;
 if (asList != null)
 {
 return asList;
 }
 var list = new List<string>();
 var asString = Audience as string;
 if (asString != null)
 {
 list.Add(asString);
 }
 
 return list;
 }
 }
 }
 }
 }