implementing client certificate support

[Sean Conner]

It was thus said that the Great Tadeusz Sosnierz once stated:
> 
> 2020-06-09 22:59 GMT+02:00 Sean Conner<sean at conman.org>:
> > Just saying "bad certificate" isn't actionable enough for the user. Why
> > is it bad? Has it expired? Rejected? What? I NEED TO KNOW!
> 
> Isn't that something that could go in the "meta" part of the response, or
> the content itself?

  It could, but what does it mean when I get back "ní ghlactar le deimhniú",
"diúltaíodh deimhniú sa todhchaí", or "diúltaíodh deimhniú caite"?  Not
everyone speaks English and a numeric response is unambiguous.

> The specificness of 6x codes is something I find quite puzzling,
> especially considering how carefully select the other codes are.
> 
> Especially 64. When does that even come into play?

  Time skew between the client and server on a freshly minted certificate.  

> (Oh, and hi everyone; I'm new here, so excuse my perhaps silly questions :))

  Hello, and no, your questions aren't silly.

  -spc