C# - Iframe Canvas Application With Master Page?

I am developing an Iframe-Canvas Application.

I am using Master Page to gain permission access & display few details, that works good.

Then on content Page I want to display a textbox & linkbutton so user can post status on their wall & here I get error

(OAuthException) An active access token must be used to query information about the current user.

here's my code :

Site.master.cs
protected void Page_Load(object sender, EventArgs e)
{
var auth = new CanvasAuthorizer { Permissions = new[] { "user_about_me","user_birthday","user_location","offline_access","publish_stream" } };

[Code]....