To be able to post to this forum you need to have an account on the main OpenStreetMap website. Once you have such an account you can login with both the email address or the Display Name. In both cases the Display name is chosen as the username for this forum. Therefore you won’t be able to login on this forum in case you don’t have an Display name configured.
Below is an example of the My Settings page, the Display Name is used as the username for this forum:
If you already have an account on the forum and the username happens to be the same as the Display Name then you will keep your post history and personal settings automatically. If you are new to the forum, or your username differs from the Display Name, a new account is immediately created for you in the forum database.
If a new account is created for you while you already had an account on the forum, please do not hesitate to contact me. Your old posts can be moved over to the new account with a few hacks in the database.
If you have problems trying to login where the forum reports ‘succesfully logged-in’, redirects and then appears to be logged-out: Please delete the cookie named ‘forum.openstreetmap.org’ from your browser cache and try again. That should fix it.
Would it be a cool function to have an automatic link to your position on a map in the personal information section (the bit on the left of each post, just like the E-mail or Website link)? I think that could be easily added based on the info returned by the authentication request…