Changing the email address before any email address is activated should
be subject to a different rate limit than the normal activation email
resending. If there's only one rate limit for both, then if a newly
signed up quickly discovers they gave a wrong email address, they'd have
to wait three minutes to change it.
With the two separate limits, they don't - but they'll have to wait
three minutes before they can change the email address again.
The downside of this setup is that a malicious actor can alternate
between resending and changing the email address (to something like
`user+$idx@domain`, delivered to the same inbox) to effectively halving
the rate limit. I do not think there's a better solution, and this feels
like such a small attack surface that I'd deem it acceptable.
The way the code works after this change is that `ActivatePost` will now
check the `MailChangeLimit_user` key rather than `MailResendLimit_user`,
and if we're within the limit, it will set `MailChangedJustNow_user`. The
`Activate` method - which sends the activation email, whether it is a
normal resend, or one following an email change - will check
`MailChangedJustNow_user`, and if it is set, it will check the rate
limit against `MailChangedLimit_user`, otherwise against
`MailResendLimit_user`, and then will delete the
`MailChangedJustNow_user` key from the cache.
Fixes#2040.
Signed-off-by: Gergely Nagy <forgejo@gergo.csillger.hu>
e35d2af2e5