Use secure TLS/SSL versions:

TLS1.2 can be used instead, it is available in all currently
supported versions of OpenSSL.

Signed-off-by: Damian Jarek <damian.jarek93@gmail.com>

example/advanced/server-flex/advanced_server_flex.cpp

@@ -971,7 +971,7 @@ int main(int argc, char* argv[])
     net::io_context ioc{threads};
 
     // The SSL context is required, and holds certificates
-    ssl::context ctx{ssl::context::sslv23};
+    ssl::context ctx{ssl::context::tlsv12};
 
     // This holds the self-signed certificate used by the server
     load_server_certificate(ctx);