Error Getting Access Token on SharePoint 2010 development

Hi to all,

I implemented the sample proposed in the link :

http://msdn.microsoft.com/en-us/library/hh454950.aspx

This works flawless on a console application, when i tryed to implement on SharePoint 2010 (specifically in an IHttpHandler '.ashx'file) i getting the error bellow on webRequest.GetRequestStream()

Error :

The underlying connection was closed: Could not establish trust relationship for the SSL/TLS secure channel.
at System.Net.HttpWebRequest.GetRequestStream(TransportContext& context)
   at System.Net.HttpWebRequest.GetRequestStream()

Can anyone help me ?

Regards!

SharePoint Solution Architect