EDIT: Hey everyone! Thanks for hanging in with us, we had a little bit of an issue authenticating sessions due to a breaking Valve change that we were surprised with about four hours ago. If you're trying to log in to sites like Scrap.tf or TF2Outpost and get an error, this is probably why.
We've fixed this on our end and have submitted a patch to the creator of the library that we use. If you're still having issues logging in, please let me know at im at alexandra dot moe.
Sorry for the inconvienence!
Original: Valve has changed the Steam login mechanism, which is returning SteamID 0. You'll know that your login failed if you have the typing Kermit GIF as your avatar. If you logged in before about 2 hours ago, you should be fine. A fix will be coming soon.