facebook c# sdk - Canvas authentication for c# asp.net and general principles -

i trying find general principles of using facebook c# sdk write canvas application.

my approach follows. have master page attempt authorise on oninit page. well. first time round not authorized , second time round are. when post goes wrong. have expected authorization / cookies / session item / viewstate item hang around , authorizer item remain authorised.

this appears not case.

should check authorization once , stick auth token in memory? when want information / post information, pass auth token in manually?

is general principle when want post / create new instance of facebookapp , pass in auth token?

here code using.

can general principles specific c#, asp.net, codeplex sdk dlls

many spiggers

public partial class facebook : system.web.ui.masterpage {     protected facebookapp fbapp;     protected canvasauthorizer authorizer;     protected facebooksettings osettings = new facebooksettings();      protected override void oninit(eventargs e) {              //not sure need this, or indeed if works             //httpcontext.current.response.addheader("p3p", "cp=\"idc dsp cor adm devi taii psa psd ivai ivdi coni our ind cnt\"");              osettings.appid = config.facebook.facebookapplicationid;             osettings.appsecret = config.facebook.facebooksecret;             fbapp = new facebookapp(osettings);             authorizer = new canvasauthorizer(fbapp);              if (!authorizer.isauthorized()) // postbacks fail this, reposts , postback event not fire!!!             {                 string scope = "publish_stream,email,user_birthday";                 var url = common.facebook.authorization.authurl(config.facebook.facebookapplicationid, config.facebook.redirecturl, scope);                 var content = canvasurlbuilder.getcanvasredirecthtml(url);                 response.contenttype = "text/html";                 response.write(content);                 response.end();             }             base.oninit(e);         }      }