This is suprisingly fun. At first, you feel like a badass, reading the documentation for every function call, googling for exotic bugs. Then you feel like a total idiot when you notice how simple it actually is. Finally, you laugh at people in the IRC because you know exactly how stupid they feel.
Yeah... I can't believe I spent time looking for something wrong with the HMAC used for session cookies. Also, I'm pretty sure I solved #5 the "wrong" way since it didn't actually involve the hint they gave.