Auth loop in facebook

i am new in Developing开发者_开发技巧 Facebook App.I just saw a tutorial on facebook and start developing the App.Everything was going fine but when i click on App the App goes in an infinite loop of Authentication and web address keep on incrementing the auth part.I had seen 100 of tutorials on developing facebook app but all of them goes into an infinte loop.what could be the reason?Anyone please let me know.Some people say it as White Screen of Death

When user comes to your canvas, then you look for the signed_request including access token otherwise you redirect to authorization page, then use grants authorization it come backs to your canvas, here:
somehow you can't get the access token, the loop starts.