Hi,
someone else can (and hopefully will) write more words on that matter
but I’m just writing it here today so we don’t forget if this ever
goes to LC again.
There is currently no way to discover that a server is 'invite only'.
Both register and 0445 have stream features but there is no way to
discover that 0445 is "required" for <register/> to work. There is
also no standardized error message for the registration in case that
fails due to missing token submission. I think both should exists.
cheers
Daniel