It has to: if it did 100% of the post-accept(2) work in a subprocess it would be pretty easy to remotely forkbomb/PID-exhaust a system by spamming invalid logins.

> You cannot avoid "I forgot to check for an error"

Yes you can. Checked exceptions and tagged unions both force calling code to be written with error-awareness.

In SSH's case, "I forgot to check" might lead to crashes (which might knock over sshd so new connections are impossible), or it might lead to false-positives via comparing NULL == NULL.

I'd much rather that boneheaded API users have to write code like

    resultstruct x = authenticate_user(user)
    if x.haserror {
        rv = { .user = user, .result = "successfully authenticated" } 
    } else {
        rv = { .user = user, .result = x.result }
    }
    return rv