mod_ssl: Log private key material to file set by $SSLKEYLOGFILE in the environment, using the standard format which can be parsed by (e.g.) wireshark for decoding SSL/TLS traffic; supported from OpenSSL 1.1.1.
* modules/ssl/ssl_private.h: Add keylog_file to SSLModConfigRec.
* modules/ssl/ssl_engine_init.c (ssl_init_Module): Open log file if SSLKEYLOGFILE is set in the environment. (ssl_init_ctx_protocol): Register the keylog callback with OpenSSL.
* modules/ssl/ssl_engine_kernel.c (modssl_callback_keylog): New function.