diff --git a/lib/src/auth/wampcra.dart b/lib/src/auth/wampcra.dart
index e48b9aa..beff6e3 100644
--- a/lib/src/auth/wampcra.dart
+++ b/lib/src/auth/wampcra.dart
@@ -7,7 +7,7 @@ import "package:wampproto/messages.dart";
 import "package:wampproto/src/auth/auth.dart";
 
 class WAMPCRAAuthenticator extends IClientAuthenticator {
-  WAMPCRAAuthenticator(this._secret, String authID, Map<String, dynamic> authExtra) : super(type, authID, authExtra);
+  WAMPCRAAuthenticator(this._secret, String authID, [Map<String, dynamic>? authExtra]) : super(type, authID, authExtra);
 
   static const String type = "wampcra";
   final String _secret;
@@ -47,7 +47,8 @@ String generateWampCRAChallenge(int sessionID, String authID, String authRole, S
 }
 
 String signWampCRAChallenge(String challenge, Uint8List key) {
-  return Hmac(sha256, key).convert(utf8.encode(challenge)).toString();
+  final signature = Hmac(sha256, key).convert(utf8.encode(challenge));
+  return base64.encode(signature.bytes);
 }
 
 bool verifyWampCRASignature(String signature, String challenge, Uint8List key) {
diff --git a/test/auth/wampcra_test.dart b/test/auth/wampcra_test.dart
index 5a027c0..48d8cff 100644
--- a/test/auth/wampcra_test.dart
+++ b/test/auth/wampcra_test.dart
@@ -9,7 +9,7 @@ void main() {
   const craChallenge = '{"nonce":"cdcb3b12d56e12825be99f38f55ba43f","authprovider":"provider","authid":"foo",'
       '"authrole":"admin","authmethod":"wampcra","session":123,"timestamp":"2024-05-07T09:25:13.307Z"}';
   const key = "6d9b906ad60d1f4dd796dbadcc2e2252310565ccdc6fe10b289df5684faf2a46";
-  const validSignature = "0c854bddb2acfc48bdd5e4326339f352a12c893997ef4e413445ee89c3698bc0";
+  const validSignature = "DIVL3bKs/Ei91eQyYznzUqEsiTmX705BNEXuicNpi8A=";
 
   group("WAMPCRAAuthenticator", () {
     test("authenticate", () {