How to make OpenSSL as the TLS backend on Windows and macOS?

> ssl: Enable SSL/TLS support using the platform-default TLS backend. On Windows this is [Schannel](https://docs.microsoft.com/en-us/windows/win32/com/schannel), on macOS [Secure Transport](https://developer.apple.com/documentation/security/secure_transport), and [OpenSSL](https://www.openssl.org/) (or equivalent) on all other platforms. Enabled by default.

Thanks for your work on the project. Is there a way to make `OpenSSL` as the TLS backend on all platforms?