Github user vgotra commented on the issue:
https://github.com/apache/thrift/pull/1449
@jeking3 - pls check what version of mono is used for building csharp - it
seems it very old (because it doesn't contain Tls11 and Tls12 in enumeration -
error `System.Security.Authentication.SslProtocols' does not contain a
definition for `Tls11')---
