diff --git a/lib/messages.dart b/lib/messages.dart
index f4dfc10..8033cbc 100644
--- a/lib/messages.dart
+++ b/lib/messages.dart
@@ -6,7 +6,7 @@ export "src/messages/challenge.dart" show Challenge;
 export "src/messages/error.dart" show Error;
 export "src/messages/event.dart" show Event;
 export "src/messages/goodbye.dart" show Goodbye;
-export "src/messages/hello.dart" show Hello;
+export "src/messages/hello.dart" show Hello, IHelloFields;
 export "src/messages/interrupt.dart" show Interrupt;
 export "src/messages/invocation.dart" show Invocation;
 export "src/messages/message.dart" show Message;
diff --git a/lib/src/joiner.dart b/lib/src/joiner.dart
index 0a93a37..231b5ba 100644
--- a/lib/src/joiner.dart
+++ b/lib/src/joiner.dart
@@ -2,6 +2,7 @@ import "package:wampproto/auth.dart";
 import "package:wampproto/messages.dart";
 import "package:wampproto/serializers.dart";
 import "package:wampproto/src/exception.dart";
+import "package:wampproto/src/messages/hello.dart";
 import "package:wampproto/src/types.dart";
 
 final clientRoles = <String, Map<String, Map>>{
@@ -29,11 +30,13 @@ class Joiner {
 
   Object sendHello() {
     final hello = Hello(
-      _realm,
-      clientRoles,
-      _authenticator.authID,
-      [_authenticator.authMethod],
-      authExtra: _authenticator.authExtra,
+      HelloFields(
+        _realm,
+        clientRoles,
+        _authenticator.authID,
+        [_authenticator.authMethod],
+        authExtra: _authenticator.authExtra,
+      ),
     );
 
     _state = stateHelloSent;
diff --git a/lib/src/messages/hello.dart b/lib/src/messages/hello.dart
index cf5d849..f17d116 100644
--- a/lib/src/messages/hello.dart
+++ b/lib/src/messages/hello.dart
@@ -2,9 +2,45 @@ import "package:wampproto/src/messages/message.dart";
 import "package:wampproto/src/messages/util.dart";
 import "package:wampproto/src/messages/validation_spec.dart";
 
+abstract class IHelloFields {
+  String get realm;
+
+  Map<String, dynamic> get roles;
+
+  String get authID;
+
+  List<dynamic> get authMethods;
+
+  Map<String, dynamic> get authExtra;
+}
+
+class HelloFields implements IHelloFields {
+  HelloFields(this._realm, this._roles, this._authid, this._authmethods, {Map<String, dynamic>? authExtra})
+      : _authextra = authExtra ?? {};
+  final String _realm;
+  final Map<String, dynamic> _roles;
+  final String _authid;
+  final List<dynamic> _authmethods;
+  final Map<String, dynamic> _authextra;
+
+  @override
+  String get realm => _realm;
+
+  @override
+  Map<String, dynamic> get roles => _roles;
+
+  @override
+  String get authID => _authid;
+
+  @override
+  List<dynamic> get authMethods => _authmethods;
+
+  @override
+  Map<String, dynamic> get authExtra => _authextra;
+}
+
 class Hello implements Message {
-  Hello(this.realm, this.roles, this.authID, this.authMethods, {Map<String, dynamic>? authExtra})
-      : authExtra = authExtra ?? {};
+  Hello(this._helloFields);
 
   static const int id = 1;
   static const String text = "HELLO";
@@ -19,11 +55,17 @@ class Hello implements Message {
     },
   );
 
-  final String realm;
-  final Map<String, dynamic> roles;
-  final String authID;
-  final List<dynamic> authMethods;
-  final Map<String, dynamic> authExtra;
+  final IHelloFields _helloFields;
+
+  String get realm => _helloFields.realm;
+
+  Map<String, dynamic> get roles => _helloFields.roles;
+
+  String get authID => _helloFields.authID;
+
+  List<dynamic> get authMethods => _helloFields.authMethods;
+
+  Map<String, dynamic> get authExtra => _helloFields.authExtra;
 
   static Hello parse(final List<dynamic> message) {
     var fields = validateMessage(message, id, text, _validationSpec);
@@ -45,7 +87,7 @@ class Hello implements Message {
       authExtra = validateMapOrRaise(fields.details!["authextra"], text, "authextra");
     }
 
-    return Hello(fields.realm!, roles, authid, authMethods, authExtra: authExtra);
+    return Hello(HelloFields(fields.realm!, roles, authid, authMethods, authExtra: authExtra));
   }
 
   @override