I have the same error, I’ve been using the engine for months and the launcher hasn’t failed once. I tried changing DNS server, no luck.
The launcher updated right before the issue started to occur, so I suspect that’s it’s either a bad update or too many people trying to use the launcher since the announcement today. Although, it’s clearly not affecting everyone, so maybe the problem is only affecting those on a specific platform or in a region. Are you in the UK too? Maybe there’s a different account authentication server here.
I’m pretty sure someone will fix this on the back end eventually.