Unity: Mono.Security.Interface.TlsException: Verification failure during handshake

I’ve created web-sockets server in unity and my client is HTML game.
Since game is going to work in browsers I want to run on SSL and gamelift has the option to attach certificates available on the intances.
The websocket server starts properly but when the HTML client tries to connect the server, the server thows error

Failed to Authenticate System.Security.Authentication.AuthenticationException: A call to SSPI failed, see inner exception. ---> Mono.Security.Interface.TlsException: Verification failure during handshake
  at Mono.Unity.UnityTlsContext.ProcessHandshake () [0x00081] in <c8c8707b2adc41b09ae682df75fe1fd0>:0 
  at Mono.Net.Security.MobileAuthenticatedStream.ProcessHandshake (Mono.Net.Security.AsyncOperationStatus status) [0x0003e] in <c8c8707b2adc41b09ae682df75fe1fd0>:0 
  at (wrapper remoting-invoke-with-check) Mono.Net.Security.MobileAuthenticatedStream.ProcessHandshake(Mono.Net.Security.AsyncOperationStatus)
  at Mono.Net.Security.AsyncHandshakeRequest.Run (Mono.Net.Security.AsyncOperationStatus status) [0x00006] in <c8c8707b2adc41b09ae682df75fe1fd0>:0 
  at Mono.Net.Security.AsyncProtocolRequest+<ProcessOperation>d__24.MoveNext () [0x000ff] in <c8c8707b2adc41b09ae682df75fe1fd0>:0 

It looked like issue with the CA certificate.
But I have tried my same web-socket code with .net framework it works.
So it has to do something with the unity.
While googling about this I came across something called mono certificate store.
I said that mono handles its own certificate store. so how can i import the rootCertificate.pem given by gamelift import in the mono certificate store.

I may be completely wrong about this but can anyone guide me on this. how can this be solved.