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

Src/GoogleApis.Auth/OAuth2/IAccessMethod.cs

Index: Src/GoogleApis.Auth/OAuth2/IAccessMethod.cs
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new file mode 100644
--- /dev/null
 b/Src/GoogleApis.Auth/OAuth2/IAccessMethod.cs
@@ -0,0 1,25 @@
 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 specified 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);
 }
 }