Reset rather than nil out Authenticator

For reuse in control channel.

TunnelKit/Sources/Protocols/OpenVPN/Authenticator.swift

@@ -62,9 +62,9 @@ extension OpenVPN {
 
         private(set) var serverRandom2: ZeroingData?
 
-        let username: ZeroingData?
+        private(set) var username: ZeroingData?
         
-        let password: ZeroingData?
+        private(set) var password: ZeroingData?
         
         var withLocalOptions: Bool
         
@@ -87,6 +87,17 @@ extension OpenVPN {
             controlBuffer = Z()
         }
         
+        func reset() {
+            controlBuffer.zero()
+            preMaster.zero()
+            random1.zero()
+            random2.zero()
+            serverRandom1?.zero()
+            serverRandom2?.zero()
+            username = nil
+            password = nil
+        }
+        
         // MARK: Authentication request
 
         // Ruby: on_tls_connect

TunnelKit/Sources/Protocols/OpenVPN/OpenVPNSession.swift

@@ -745,7 +745,7 @@ public class OpenVPNSession: Session {
     
     private func completeConnection() {
         setupEncryption()
-        authenticator = nil
+        authenticator?.reset()
         negotiationKey.controlState = .connected
         connectedDate = Date()
         transitionKeys()