server/tls: Do not rely on a specific cipher suite (#4021)

Do not rely on a specific cipher suite instead let the
go choose the type of cipher needed, if the connection
is coming from clients which do not support forward
secrecy let the go tls handle this automatically based
on tls1.2 specifications.

Fixes #4017

cmd/server-mux.go

@@ -401,23 +401,8 @@ func (m *ServerMux) ListenAndServe(certFile, keyFile string) (err error) {
 		// Causes servers to use Go's default ciphersuite preferences,
 		// which are tuned to avoid attacks. Does nothing on clients.
 		PreferServerCipherSuites: true,
-		// Only use curves which have assembly implementations
-		CurvePreferences: []tls.CurveID{
-			tls.CurveP256,
-		},
 		// Set minimum version to TLS 1.2
 		MinVersion: tls.VersionTLS12,
-		CipherSuites: []uint16{
-			tls.TLS_ECDHE_ECDSA_WITH_AES_256_GCM_SHA384,
-			tls.TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384,
-			tls.TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256,
-			tls.TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256,
-
-			// Best disabled, as they don't provide Forward Secrecy,
-			// but might be necessary for some clients
-			// tls.TLS_RSA_WITH_AES_256_GCM_SHA384,
-			// tls.TLS_RSA_WITH_AES_128_GCM_SHA256,
-		},
 	} // Always instantiate.
 
 	if tlsEnabled {