Do prisoners have a right to religious freedom?

I recently saw an article about a prisoner suing for the right to worship the Flying Spaghetti Monster, as well as another about an upcoming Supreme Court case for a Muslim who would like to grow his beard longer than rules allow. My question is, how much should prisons accommodate religion? Anyone could say anything is part of their religion, e.g., "My religion states we do not believe in prisons. Therefore, I should be set free." Where should the line be drawn in the sand? Do prisoners have any right to religious freedom?