http://l3tczdiiwoo63iwxty4lhs6p7eaxop5micbn7vbliydgv63x5zrrrfyd.onion/user-manual/howto.html
You can choose between LibreSSL , MbedTLS , OpenSSL and wolfSSL . Which TLS library is the best choice depends on various factors including operating system,
cpu and license preference so there isn't any recommendation here.