Old boost versions lack of generic TLS support
The 2017/03/05 a "generic TLS" method was added to boost/asio/ssl/context_base.hpp which maps the OpenSSL TLS_method() described in the SSL_CTX_NEW manual page.
This ticket does two things:
- as an emergency measure switch to tlsv12 from tls.
- detects the support of the boost::asio::ssl::context::tls method in configure
Note the documentation should be updated to recommend to use a boost version with the support i.e. at least 1.64.0