boost::asio::io_service io;
boost::asio::ssl::context ctx(boost::asio::ssl::context::sslv23_client);
boost::asio::ssl::stream<boost::asio::ip::tcp::socket> backend(io, ctx);

// need some object that will store the cache
std::map<std::string, SSL_SESSION*> ssl_cache;

// add session to the cache after a successful connection
SSL_SESSION *session = SSL_get1_session(backend.native_handle());
ssl_cache[host] = session;

// before a new connection to the 'host', check the cache
auto cached_session = ssl_cache.find(host);
if (cached_session != ssl_cache.end())
{
    SSL_SESSION *session = cached_session->second;
    SSL_set_session(backend.native_handle(), session);
}

// after a connection can check if ssl-session was reused
if (SSL_session_reused(backend.native_handle()))
{
    // reused
}