Me di cuenta de que esta pregunta se había formulado anteriormente, pero con poco código de ejemplo, así que vuelvo a preguntar pero con al menos un poco de orientación.

Después de horas de búsqueda, he encontrado la siguiente implementación parcial.

namespace GoogleAnalyticsAPITest.Console
{
    using System.Security.Cryptography.X509Certificates;
    using DotNetOpenAuth.OAuth2;
    using Google.Apis.Analytics.v3;
    using Google.Apis.Analytics.v3.Data;
    using Google.Apis.Authentication.OAuth2;
    using Google.Apis.Authentication.OAuth2.DotNetOpenAuth;

    class Program
    {
        static void Main(string[] args)
        {
            log4net.Config.XmlConfigurator.Configure();
            string Scope = Google.Apis.Analytics.v3.AnalyticsService.Scopes.Analytics.ToString().ToLower();
            string scopeUrl = "https://www.googleapis.com/auth/" + Scope;
            const string ServiceAccountId = "nnnnnnnnnnn.apps.googleusercontent.com";
            const string ServiceAccountUser = "[email protected]";
            AssertionFlowClient client = new AssertionFlowClient(
                GoogleAuthenticationServer.Description, new X509Certificate2(@"7039572692013fc5deada350904f55bad2588a2a-privatekey.p12", "notasecret", X509KeyStorageFlags.Exportable))
            {
                Scope = scopeUrl,
                ServiceAccountId = ServiceAccountId//,ServiceAccountUser = ServiceAccountUser
            };
            IAuthorizationState state = AssertionFlowClient.GetState(client);
            AnalyticsService service = new AnalyticsService(authenticator);
            string profileId = "ga:xxxxxxxx";
            string startDate = "2010-10-01";
            string endDate = "2010-10-18";
            string metrics = "ga:visits";
            DataResource.GaResource.GetRequest request = service.Data.Ga.Get(profileId, startDate, endDate, metrics);
            request.Dimensions = "ga:date";
            GaData data = request.Fetch();
        }
    }
}

Tengo un par de problemas. La llamada aAssertionFlowClient.GetState(client) da como resultado una respuesta "invalid_scope" como se ve en el registro DotNetOpenAuth de

2012-10-19 13: 27: 36,272 (GMT-4) [8] INFO DotNetOpenAuth - DotNetOpenAuth, Versión = 4.0.0.11165, Cultura = neutral, PublicKeyToken = 2780ccd10d57b246 (oficial) 2012-10-19 13: 27: 36,284 ( GMT-4) [8] DEBUG DotNetOpenAuth.Messaging.Channel - Preparándose para enviar el mensaje AssertionFlowMessage (2.0). 2012-10-19 13: 27: 36,294 (GMT-4) [8] INFO DotNetOpenAuth.Messaging.Channel - Mensaje de AssertionFlowMessage (2.0) de Assertion saliente preparado parahttps://accounts.google.com/o/oauth2/token: grant_type: assertion assertion_type:http://oauth.net/grant_type/jwt/1.0/bearer Afirmación: (un montón de caracteres codificados van aquí)

2012-10-19 13: 27: 36,296 (GMT-4) [8] DEBUG DotNetOpenAuth.Messaging.Channel - Sending AssertionFlowMessage request. 2012-10-19 13: 27: 36,830 (GMT-4) [8] DEBUG DotNetOpenAuth.Http - HTTP POSThttps://accounts.google.com/o/oauth2/token 2012-10-19 13: 27: 36,954 (GMT-4) [8] ERROR DotNetOpenAuth.Http - WebException dehttps://accounts.google.com/o/oauth2/token: {"error": "invalid_scope"}

He intentado especificar uno o ambos de ServiceAccountId y ServiceAccountUser sin suerte.

En segundo lugar, incluso si obtengo un IAuthorizationState, no estoy seguro de cómo puedo obtener un autenticador IAI que pueda pasarse al constructor AnalyticsService.

El siguiente es el web.config que uso para habilitar el registro de DotNetOpenAuth.

<?xml version="1.0"?>
<configuration>
  <configSections>
    <section name="log4net" type="log4net.Config.Log4NetConfigurationSectionHandler,log4net, Version=1.2.10.0, Culture=neutral, publicKeyToken=1b44e1d426115821" />
    <!--<section name="log4net" type="log4net.Config.Log4NetConfigurationSectionHandler" requirePermission="false"/>-->
    <sectionGroup name="dotNetOpenAuth" type="DotNetOpenAuth.Configuration.DotNetOpenAuthSection, DotNetOpenAuth">
      <section name="openid" type="DotNetOpenAuth.Configuration.OpenIdElement, DotNetOpenAuth" requirePermission="false" allowLocation="true"/>
      <section name="oauth" type="DotNetOpenAuth.Configuration.OAuthElement, DotNetOpenAuth" requirePermission="false" allowLocation="true"/>
      <section name="messaging" type="DotNetOpenAuth.Configuration.MessagingElement, DotNetOpenAuth" requirePermission="false" allowLocation="true"/>
      <section name="reporting" type="DotNetOpenAuth.Configuration.ReportingElement, DotNetOpenAuth" requirePermission="false" allowLocation="true"/>
    </sectionGroup>
  </configSections>
  <log4net>
    <appender name="RollingFileAppender" type="log4net.Appender.RollingFileAppender">
      <file value="DotNetOpenAuth.log"/>
      <appendToFile value="true"/>
      <rollingStyle value="Size"/>
      <maxSizeRollBackups value="10"/>
      <maximumFileSize value="100KB"/>
      <staticLogFileName value="true"/>
      <layout type="log4net.Layout.PatternLayout">
        <conversionPattern value="%date (GMT%date{%z}) [%thread] %-5level %logger - %message%newline"/>
      </layout>
    </appender>
    <appender name="TracePageAppender" type="OpenIdProviderWebForms.Code.TracePageAppender, OpenIdProviderWebForms">
      <layout type="log4net.Layout.PatternLayout">
        <conversionPattern value="%date (GMT%date{%z}) [%thread] %-5level %logger - %message%newline"/>
      </layout>
    </appender>
    <!-- Setup the root category, add the appenders and set the default level -->
    <root>
      <level value="ALL"/>
      <appender-ref ref="RollingFileAppender"/>
      <appender-ref ref="TracePageAppender"/>
    </root>
    <!-- Specify the level for some specific categories -->
    <logger name="DotNetOpenAuth">
      <level value="ALL"/>
    </logger>
  </log4net>
  <dotNetOpenAuth>
    <!-- This is an optional configuration section where aspects of dotnetopenauth can be customized. -->
    <!-- For a complete set of configuration options see http://www.dotnetopenauth.net/developers/code-snippets/configuration-options/ -->
    <!--<messaging clockSkew="00:10:00" lifetime="00:03:00" strict="true">-->
    <!--<messaging>
      <untrustedWebRequest timeout="00:00:30" readWriteTimeout="00:00:01.500" maximumBytesToRead="1048576" maximumRedirections="10">
        <whitelistHosts>
          -->
    <!-- Uncomment to enable communication with localhost (should generally not activate in production!) -->
    <!--
          <add name="localhost"/>            
        </whitelistHosts>
      </untrustedWebRequest>
    </messaging>-->
    <!-- Allow DotNetOpenAuth to publish usage statistics to library authors to improve the library. -->
    <reporting enabled="false"/>
  </dotNetOpenAuth>
  <appSettings>
    <!--<add key="log4net.Internal.Debug" value="true" />-->
  </appSettings>
  <runtime>
  </runtime>
  <startup>
    <supportedRuntime version="v4.0" sku=".NETFramework,Version=v4.0"/>
  </startup>
</configuration>