For around 2 weeks, I've been getting an increasing quantity of nonspecific
reports from users of login problems on ikiwiki sites, mostly joeyh.name
and git-annex.branchable.com. A few users are still logging in
successfully, but it seems to be hitting many users; post volume has gone
down more than holidays would explain.

It doesn't seem limited to any login method; email and password have both
been said not to work. (Openid too, but could be openid provider problem
there.)

I have not managed to reproduce the problem myself, using firefox,
firefox-esr, or chromium. --[[Joey]]

> Otto Kekäläinen described to me a problem where email login to post a
> comment seemed to work; it displayed the comment edit form; but posting
> the form went back to the login page. Cookie problem?
> 
> Ok, to reproduce the problem: Log into joeyh.name using https. The email
> login link is a http link. The session cookie was set https-only.
> --[[Joey]]
> 
> The reason the edit form is able to be displayed is that emailauth
> sets up a session, in getsession(), and that $session is used for the
> remainder of that cgi call. But, a cookie for that session is not stored
> in the browser in this case. Ikiwiki *does* send a session cookie, but
> the browser seems to not let an existing https-only session cookie be
> replaced by a new session cookie that can be used with http. (If the
> emailed link, generated on https is opened in a different browser, this
> problem doesn't happen.) There may have been a browser behavior change
> here?
> 
> So what to do about this? Sites with the problem have `redirect_to_https: 0`
> and the cgiurl is http not https. So when emailauth generates the url
> with `cgiurl_abs`, it's a http url, even if the user got to that point
> using https.
> 
> I suppose that emailauth could look at `$ENV{HTTPS}` same as
> printheader() does, to detect this case, and rewrite the cgiurl as a
> https url. Or, printheader() could just not set "-secure" on the cookie,
> but that does degrade security as MITM can then steal the cookie you're
> using on a https site.
> 
> Of course, the easy workaround, increasingly a good idea anyway, is to
> enable `redirect_to_https`.. --[[Joey]]

> One of the users also reported a problem with password reset, and
> indeed, passwordauth is another caller of `cgiurl_abs`. (The only other
> caller, notifyemail, is probably fine.) The emailed password reset link
> also should be https if the user was using https. So, let's add a
> `cgiurl_abs_samescheme` that both can use. --[[Joey]]

[[fixed|done]].. At least I hope that was the thing actually preventing most
of the people from logging in. --[[Joey]]