Sam Crabtree shares an astute insight from an Arab, underground blogger he met last year:
Jesus informs his disciple, Simon Peter, that Satan has demanded permission to sift him as wheat. In Job chapter 1, we see Satan complaining that God has built a hedge of protection around Job so that Satan can do nothing to harm Job. Satan has to ask permission from God to harm Peter and Job, and it was necessary for God to remove his hand of protection from them both so that Satan could afflict them.
I think we can safely assume there are many such times that Satan demands to do likewise to us.