Support Reading Certificate in PKCS12 file format (.p12)

[vanstee]

It would be nice if you could just hand over the .p12 certificate that Apple provides, instead of having to convert it to a .pem.

NOTE: @kyledrake: "however using the PKCS12 class directly will break JRuby support, which does not have this class available."

This was spun out of #13.

Thanks for bringing this up @betamatt, @linjunpop, and @kyledrake.

[kyledrake]

Related: jruby/jruby-ossl#8

[kyledrake]

This is not ideal, but here is some code to use a command line for processing with JRuby. We've been using it internally so I know it works. https://gist.github.com/3077989

This code example would add a dependency on Escape, but it would be trivial to remove that dependency and not use it.

[vanstee]

I think we should probably just not accept the PKCS12 format when using jruby. I'd rather just have jruby users do the conversion on their own (especially since Apple recommends that anyway). :/

I'll follow jruby/jruby-ossl#8 and include it once jruby supports it.

I might be open to other methods of doing this though. Shelling out just seems really dirty to me.

[kyledrake]

Oh, it's totally dirty. And there might be security implications for some users too. I'd rather just provide users the instructions to do the conversion themselves in that case.