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We now have our own login system, rather than exclusively allowing logins via GitHub. We're hoping this allows more people to sign up and use CodePen - specifically people who don't have and don't wish to have a GitHub account.
GitHub accounts are free and allow you to do some neat things like save out your Pen's a GitHub Gist's. But we didn't want people to see "Git", think of all that complexity, and think CodePen isn't for them. Using CodePen is a lot simpler (and doesn't have much to do with) version control. Now we aren't totally reliant on a third party for uptime as well, which is very good. Both login methods will be sticking around.
You can also change your username directly on CodePen now, which wasn't possible before.
Login happens over SSL, so we're nice and secure. We originally wanted to have login be a popup modal so you could do it from any page (like you could with the GitHub only login), but because login must be SSL to be properly secure, we needed the login page to be always on HTTPS. You can't make an HTTPS Ajax call from an HTTP parent page. We could just redirect you after submission but that's makes errors states kinda janky. Thus, the specific login page.
We do take care to direct you back to where you came from after logging in though, so the experience is almost the same.