Boost C++ Libraries

...one of the most highly regarded and expertly designed C++ library projects in the world. — Herb Sutter and Andrei Alexandrescu, C++ Coding Standards

This is an older version of Boost and was released in 2013. The current version is 1.91.0.

error::ssl_category

static const boost::system::error_category & ssl_category = boost::asio::error::get_ssl_category();