如何在ASP.NET中使用log4net在日志文件中包含SessionID？

Install-Package log4net

 <configSections>
   <section name="log4net" type="log4net.Config.Log4NetConfigurationSectionHandler, log4net"/>
  </configSections>
  <log4net>
    <appender name="RollingFileAppender" type="log4net.Appender.RollingFileAppender">
      <file value="logs/log.txt" />
     <appendToFile value="true" />
     <rollingStyle value="Size" />
      <maxSizeRollBackups value="10" />
     <maximumFileSize value="10MB" />
     <staticLogFileName value="true" />
     <layout type="log4net.Layout.PatternLayout">
        <conversionPattern value="%date [%thread] %-5level %logger - %message%newline" />
      </layout>
    </appender>
    <root>
     <level value="DEBUG" />
      <appender-ref ref="RollingFileAppender" />
    </root>
  </log4net>
</configuration>

using log4net;

public class Global : System.Web.HttpApplication
{
    private static readonly ILog log = LogManager.GetLogger(typeof(Global));

    protected void Application_Start(object sender, EventArgs e)
    {
        log4net.Config.XmlConfigurator.Configure();
    }
}

using log4net;

public class SomeClass
{
    private static readonly ILog log = LogManager.GetLogger(typeof(SomeClass));

    public void SomeMethod()
    {
        log.Info("SessionID: " + HttpContext.Current.Session.SessionID);
    }
}