Profile username validation on meetup application form

[hlashbrooke]

We often receive meetup applications that contain invalid or non-existent WordPress.org usernames. These all come from the application form here: ​https://central.wordcamp.org/meetup-organizer-application/

It would be great if we could add some validation on that form that checks if the username exists (simply checking if the profile URL exists should be sufficient) and then, if it does not, prevents submission and directs the applicant to create a profile first.

[RMarks]

I ran into this a related problem today on the applicant's Slack username. At the very least, I'd like to suggest the username not have the @ symbol as a prefix.

For the original scenaio that @hlashbrooke reported, would we just look for the HTTP response code after accessing the user's profile? If it's a 200, allow the form to be submitted. If it's a 404, prevent the form from being submitted and show an message requesting they check their username or register for an account.

[iandunn]

I think this was fixed by ​https://github.com/WordPress/wordcamp.org/commit/92c0c72da94ba0ea9d93665ab2261455e81c4abe#diff-31d28ac8b089034ed639e52e6231e897 awhile back, but please reopen if not.