Enable for build by selecting -DLWS_WITH_SECURE_STREAMS=1 -DLWS_WITH_SECURE_STREAMS_CPP=1 at cmake.
Because it's designed for OpenSSL + system trust bundle, the minimal example minimal-secure-streams-cpp requires -DLWS_WITH_MINIMAL_EXAMPLES=1 -DLWS_WITH_MBEDTLS=0
By default the -cpp example downloads https://warmcat.com/test-a.bin to the local file /tmp/test-a.bin. By giving, eg, -c 4, you can run four concurrent downloads of files test-a.bin through test-d.bin... up to 12 files may be downloaded concurrently.
By default it will connect over h2 and share the single connection between all the downloads.
#include <libwebsockets.hxx> ... new lssFile(context, "https://warmcat.com/index.html", "/tmp/index.html", lss_completion, 0);
This will copy the remote url to the given local file, and call the completion callback when it has succeeded or failed.