The code is his birthday written as MMDDYY.
His dialogue hints at what the month/day are, so you may have to do a bit of math. Checking Sam's calendar in his room will also tell you the current (in-game) date as reference.
Just in time for Halloween, it's a game about Christmas starring everyone's favorite text-to-speech stick figure, Microsoft Sam!
It's two nights before Christmas Day, 2025, and Sam realizes he forgot to buy presents for the mandatory office Christmas party! Due to spending all his remaining money on "absolute necessities", a broke Sam sets out to the newly-opened mall in hopes of using his wit and cunning to acquire gifts another way while avoiding the watchful eye of a strange fellow in sunglasses. Absolutely nothing else weird happens in the game I promise. :)