Pottermore before it opens to everyone in October. Today I was lucky (on Day 5/7) because my friend texted me as soon as it went up so I was able to sign up, but yesterday I had a terrible time trying to get in! The window for the clue was anytime between 6:30 and 10:30 AM Pacific time (I think), so I woke up at 6, 6:30, 7, 7:20, and 8:10. Unfortunately, the clue had been up and all the spots had been filled during that last 50-minute period downtime.
Thank you to Kat (C.), remembering that the Order of the Phoenix headquarters was at 12 Grimmauld Place, and the magical quill at the top of the Scholastic website.