[PATCH 6 of 8] sslutil: document the Apple Python cert trick

[Yuya Nishihara]

On Fri, 01 Jul 2016 19:57:42 -0700, Gregory Szorc wrote:
> # HG changeset patch
> # User Gregory Szorc <gregory.szorc at gmail.com>
> # Date 1467427907 25200
> #      Fri Jul 01 19:51:47 2016 -0700
> # Node ID 17d67895b215c5c977d2b446611abb219160a6f9
> # Parent  101e040f8b014fe938803c68b502e7b72b4726f8
> sslutil: document the Apple Python cert trick
> 
> This is sort of documented in _plainapplypython()'s docstring. But
> it helps to be explicit in security code.
> 
> diff --git a/mercurial/sslutil.py b/mercurial/sslutil.py
> --- a/mercurial/sslutil.py
> +++ b/mercurial/sslutil.py
> @@ -438,16 +438,19 @@ def _defaultcacerts(ui):
>      with demandimport.deactivated():
>          try:
>              import certifi
>              ui.debug('using ca certificates from certifi\n')
>              return certifi.where()
>          except Exception:
>              pass
>  
> +    # Apple's Python has patches that allow a specially constructed certificate
> +    # to load the system CA store. If we're running on Apple Python, use this
> +    # trick.

IIRC, Python isn't patched, but OpenSSL is, and Apple Python doesn't provide
a sane way to load certificates from the patched OpenSSL. I don't know that
makes a difference on OS X, though.