SSL certificate pinning about cpr

[COM8]

@arekmula thanks for reporting!
You are right, there is no real support for it yet. But I will try to add support for it over the weekend if everything goes as planed.
The Interface would than look something like:

    /**
     * This callback function gets called by libcurl just before the initialization of an SSL connection
     * after having processed all other SSL related options to give a last chance to an application
     * to modify the behavior of the SSL initialization.
     *
     * If an error is returned from the callback no attempt to establish a connection is made
     * and the perform operation returns the callback's error code.
     * For no error return CURLE_OK from inside 'curl/curl.h'
     *
     * More/Source: https://curl.se/libcurl/c/CURLOPT_SSL_CTX_FUNCTION.html
     **/
    void SetSslCtxCallback(const SslCtxCallback& ssl_ctx);

Resulting in something like:

std::function<CURLcode(const std::shared_ptr<CurlHolder>& curl_holder, void* ssl_ctx, intptr_t userdata)>

for your custom callback.

[arekmula]

I have it already implemented and tested on my side. I can raise the MR. I would only need to adapt the API slightly to your proposed one and cover it with tests.

[arekmula]

Raised the WIP Pull request: #1020

I was not sure about passing the CurlHolder. There's no constructor of CurlHolder accepting CURL* which I could use inside of sslCtxUserFunction. We can pass CURL* or don't pass it at all.

Tests are missing but I will try to add them tomorrow or on monday.