I'll recommend you to do the following:
First of all use the Microsoft.Net.Http package. Google.Apis depends on it, so you already have it installed.
Try to use the following code:
// Create HTTP client using ConfigurableMessageHandler. // More details available in: http://contrib.google-api-dotnet-client.googlecode.com/hg/1.8.0-rc/documentation/classGoogle_1_1Apis_1_1Http_1_1ConfigurableMessageHandler.html. var httpClient = new HttpClientFactory().CreateHttpClient(new CreateHttpClientArgs { ApplicationName = "YOUR_APP_NAME", }); // Add your credential as interceptor. httpClient.MessageHandler.ExecuteInterceptors.Add(credential); // Create the request. var response = await httpClient.GetAsync( "https://www.googleapis.com/mapsengine/v1/projects");
I DIDN'T TEST it, but it should do the magic for you :)