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

Src/GoogleApis.Auth/OAuth2/IAccessMethod.cs

+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Net.Http;
+using System.Text;
+
+namespace Google.Apis.Auth.OAuth2
+{
+/// <summary>
+/// Method of presenting the access token to the resource server as specifie
d in·
+/// http://tools.ietf.org/html/rfc6749#section-7
+/// </summary>
+public interface IAccessMethod
+{
+/// <summary>
+/// Intercepts a HTTP request right before the HTTP request executes by
providing the access token.
+/// </summary>
+void Intercept(HttpRequestMessage request, string accessToken);
+
+/// <summary>
+/// Retrieve the original access token in the HTTP request, as provided
in the <see cref=" Intercept"/> method.
+/// </summary>
+string GetAccessToken(HttpRequestMessage request);
+}
+}