[HttpClient] Allow to configure `CURLOPT_SSLCERTTYPE` for CurlHttpClient

[smoench]

Description
Currently the HttpClient only allows PEM-files for local_cert but curl has more options (DER, ENG, P12). Unfortunately this needs to be configured via another option CURLOPT_SSLCERTTYPE.

My proposal is to add the option local_cert_type to the CurlHttpClient. This could configured manually or probably guessed by the file extension.

I don't know if it is supported by the AmpHttpClient.

[nicolas-grekas]

what about converting your der/eng/p12 certificates to pem instead? openssl has commands to do so.

[smoench]

I did that :-) But now I have two pem-files one for cert and one for private key. My use case is sending requests to apple push notification service for wallet updates. We also need to sign the wallets with an p12. With this option we would have only one file instead three.

(I could contribute this when it would be accepted)

[nicolas-grekas]

Can't you bundle them both in the same file? This should work IIRC.
I'm leaning toward a 👎 on this since it will create portability issues between implementations (making it more complex to move from curl to native or amp)

[smoench]

Closing for keeping portability. Feel free to open again when those client implementation will support p12 certificates.