diff --git a/src/main/java/com/ysoft/geecon/webauthn/MyWebAuthnSetup.java b/src/main/java/com/ysoft/geecon/webauthn/MyWebAuthnSetup.java
index d79ab4d..00c250a 100644
--- a/src/main/java/com/ysoft/geecon/webauthn/MyWebAuthnSetup.java
+++ b/src/main/java/com/ysoft/geecon/webauthn/MyWebAuthnSetup.java
@@ -79,7 +79,7 @@ public class MyWebAuthnSetup implements WebAuthnUserProvider {
             }
             // returning (or duplicate) user with new credential -> reject,
             // as we do not provide a means to register additional credentials yet
-            return Uni.createFrom().failure(new Throwable("Duplicate user"));
+            return Uni.createFrom().failure(new Throwable("Duplicate user: " + authenticator.getUserName()));
         }
     }
 }
\ No newline at end of file
diff --git a/src/main/resources/META-INF/resources/index.html b/src/main/resources/META-INF/resources/index.html
index e4f013c..44b31ad 100644
--- a/src/main/resources/META-INF/resources/index.html
+++ b/src/main/resources/META-INF/resources/index.html
@@ -15,41 +15,10 @@
     <script src="https://cdnjs.cloudflare.com/ajax/libs/materialize/1.0.0/js/materialize.min.js"></script>
     <script charset="UTF-8" src="/js/webauthn-debug.js" type="text/javascript"></script>
     <style>
-        .container {
-            display: grid;
-            grid-template-columns: auto auto auto;
-        }
 
-        button, input {
-            margin: 5px 0;
-        }
 
-        .item {
-            padding: 20px;
-        }
-
-        nav > ul {
-            list-style-type: none;
-            margin: 0;
-            padding: 0;
-            overflow: hidden;
-            background-color: #333;
-        }
-
-        nav > ul > li {
-            float: left;
-        }
-
-        nav > ul > li > a {
-            display: block;
-            color: white;
-            text-align: center;
-            padding: 14px 16px;
-            text-decoration: none;
-        }
-
-        nav > ul > li > a:hover {
-            background-color: #111;
+        .code {
+            white-space: pre;
         }
     </style>
 </head>
@@ -63,49 +32,36 @@
 
 <div id="trace"></div>
 
-<div class="container" id="server1">
-    <div id="server1-call"></div>
-    <div id="server1-response"></div>
+<div class="container step" id="server1">
+    The interaction starts with an AJAX call.
+    <div class="code">POST <span id="server1-url"></span>
+        <div id="server1-call"></div>
+    </div>
+    The server prepares a challenge for the browser to sign.
+    <div class="code" id="server1-response"></div>
 </div>
 
-<div class="container" id="navigator">
-    <div id="navigator-call"></div>
-    <div id="navigator-response"></div>
+<div class="container step" id="navigator">
+    The challenge is passed to the browser call:
+    <div class="code" id="navigator-call">navigator.credentials.create(...);</div>
+    Which responds:
+    <div class="code" id="navigator-response"></div>
+    The <strong>response.clientDataJSON</strong> are base64 encoded:
+    <div class="code" id="navigator-clientDataJSON"></div>
 </div>
 
-<div class="container" id="server2">
-    <div id="server2-call"></div>
-    <div id="server2-response"></div>
+<div class="container step" id="server2">
+
+    <div class="code" id="server2-call"></div>
 </div>
 </div>
 
 <div id="result"></div>
 
 <form action="#" method="POST">
-    <input id="webAuthnId" name="webAuthnId" placeholder="webAuthnId"/><br/>
-    <input id="webAuthnRawId" name="webAuthnRawId" placeholder="webAuthnRawId"/><br/>
-    <input id="webAuthnResponseAttestationObject" name="webAuthnResponseAttestationObject"
-           placeholder="webAuthnResponseAttestationObject"/><br/>
-    <input id="webAuthnResponseClientDataJSON" name="webAuthnResponseClientDataJSON"
-           placeholder="webAuthnResponseClientDataJSON"/><br/>
-    <div id="webAuthnResponseClientDataJSONJson"></div>
-    <br/>
-    <input id="webAuthnResponseAuthenticatorData" name="webAuthnResponseAuthenticatorData"
-           placeholder="webAuthnResponseAuthenticatorData"/><br/>
-    <div id="webAuthnResponseAuthenticatorDataJson"></div>
-    <br/>
-    <input id="webAuthnResponseSignature" name="webAuthnResponseSignature"
-           placeholder="webAuthnResponseSignature"/><br/>
-    <div id="webAuthnResponseSignatureJson"></div>
-    <br/>
-    <input id="webAuthnResponseUserHandle" name="webAuthnResponseUserHandle"
-           placeholder="webAuthnResponseUserHandle"/><br/>
-    <div id="webAuthnResponseUserHandleJson"></div>
-    <br/>
-
-    <input id="webAuthnType" name="webAuthnType" placeholder="webAuthnType"/><br/>
-    <button formaction="/webauthn/register" type="submit">Finish registration</button>
-    <button formaction="/webauthn/login" type="submit">Finish login</button>
+    <input name="sessionId" type="hidden" value="somesessionid">
+    <div id="form-generated"></div>
+    <button type="submit">Finish</button>
 </form>
 
 <script type="text/javascript">
@@ -129,6 +85,8 @@
     }
 
     function fillOrHideJsonField(id, value) {
+        $("#" + id).remove();
+        $
         let el = document.getElementById(id);
         if (!el) throw "No element #" + id;
         if (value !== undefined) {
@@ -141,6 +99,90 @@
 
     function tracer(stage, params) {
         console.log(stage, params)
+
+        switch (stage) {
+            case "register-request":
+                return traceRegisterRequest(params);
+            case "register-response":
+                return traceRegisterResponse(params);
+            case "credentials-create-request":
+                return traceCredentialsCreateRequest(params);
+            case "credentials-create-response":
+                return traceCredentialsCreateResponse(params);
+            case "login-request":
+                return traceLoginRequest(params);
+            case "login-response":
+                return traceLoginResponse(params);
+            case "credentials-get-request":
+                return traceCredentialsGetRequest(params);
+            case "credentials-get-response":
+                return traceCredentialsGetResponse(params);
+            default:
+                return traceGeneric(stage, params);
+        }
+    }
+
+    function continueButton(where, result) {
+        const button = $("<button>Continue</button>").appendTo(where)
+        return new Promise((resolve, reject) => {
+            button.click(() => {
+                resolve(result);
+                $(button).remove();
+            });
+        });
+    }
+
+    function traceRegisterRequest(params) {
+        $(".step").hide();
+        $("#server1").show();
+        $("#server1-url").html(params.url)
+        $("#server1-call").html(JSON.stringify(params.body, null, 2));
+        return continueButton("#server1-call", params);
+    }
+
+    function traceRegisterResponse(params) {
+        $("#server1-response").html(JSON.stringify(params, null, 2));
+        return continueButton("#server1-response", params);
+    }
+
+    function traceLoginRequest(params) {
+        $(".step").hide();
+        $("#server1").show();
+        $("#server1-url").html(params.url)
+        $("#server1-call").html(JSON.stringify(params.body, null, 2));
+        return continueButton("#server1-call", params);
+    }
+
+    function traceLoginResponse(params) {
+        $("#server1-response").html(JSON.stringify(params, null, 2));
+        return continueButton("#server1-response", params);
+    }
+
+    function traceCredentialsCreateRequest(challenge) {
+        $("#navigator").show();
+        //$("#navigator-call").html(JSON.stringify(challenge, null, 2));
+        return continueButton("#navigator-call", challenge);
+    }
+
+    function traceCredentialsCreateResponse(response) {
+        $("#navigator-response").html(JSON.stringify(response, null, 2));
+        $("#navigator-clientDataJSON").html(JSON.stringify(JSON.parse(tryDecodeBase64(response.response.clientDataJSON)), null, 2));
+        return continueButton("#navigator-response", response);
+    }
+
+    function traceCredentialsGetRequest(challenge) {
+        $("#navigator").show();
+        //$("#navigator-call").html(JSON.stringify(challenge, null, 2));
+        return continueButton("#navigator-call", challenge);
+    }
+
+    function traceCredentialsGetResponse(response) {
+        $("#navigator-response").html(JSON.stringify(response, null, 2));
+        $("#navigator-clientDataJSON").html(JSON.stringify(JSON.parse(tryDecodeBase64(response.response.clientDataJSON)), null, 2));
+        return continueButton("#navigator-response", response);
+    }
+
+    function traceGeneric(stage, params) {
         const content = JSON.stringify(params);
         const trace = $("<div class='container'></div>").attr("id", stage).html(content).appendTo("#trace");
         const button = $("<button>Continue</button>").appendTo(trace)
@@ -152,6 +194,15 @@
         });
     }
 
+    function form(action, fields) {
+        const $form = $("form").attr("action", action);
+        const $fields = $("#form-generated", $form).empty()
+        for ([key, value] of Object.entries(fields)) {
+            console.log(key);
+            $("<input type='hidden'>").attr("name", key).val(value).appendTo($fields)
+        }
+    }
+
     const webAuthn = new WebAuthn({
         callbackPath: '/q/webauthn/callback',
         registerPath: '/q/webauthn/register',
@@ -170,24 +221,15 @@
         result.replaceChildren();
         webAuthn.loginOnly({name: userName})
             .then(body => {
-                // store the registration JSON in form elements
-                fillOrHideFormField('webAuthnId', body.id);
-                fillOrHideFormField('webAuthnRawId', body.rawId);
-                fillOrHideFormField('webAuthnResponseClientDataJSON', body.response.clientDataJSON);
-                fillOrHideJsonField('webAuthnResponseClientDataJSONJson', body.response.clientDataJSON);
-                fillOrHideFormField('webAuthnResponseAuthenticatorData', body.response.authenticatorData);
-                fillOrHideFormField('webAuthnResponseSignature', body.response.signature);
-                fillOrHideFormField('webAuthnResponseUserHandle', body.response.userHandle);
-                fillOrHideFormField('webAuthnType', body.type);
-
-
-                // document.getElementById('webAuthnId').value = body.id;
-                // document.getElementById('webAuthnRawId').value = body.rawId;
-                // document.getElementById('webAuthnResponseClientDataJSON').value = body.response.clientDataJSON;
-                // document.getElementById('webAuthnResponseAuthenticatorData').value = body.response.authenticatorData;
-                // document.getElementById('webAuthnResponseSignature').value = body.response.signature;
-                // document.getElementById('webAuthnResponseUserHandle').value = body.response.userHandle;
-                // document.getElementById('webAuthnType').value = body.type;
+                form("/webauthn/login", {
+                    'webAuthnId': body.id,
+                    'webAuthnRawId': body.rawId,
+                    'webAuthnResponseClientDataJSON': body.response.clientDataJSON,
+                    'webAuthnResponseAuthenticatorData': body.response.authenticatorData,
+                    'webAuthnResponseSignature': body.response.signature,
+                    'webAuthnResponseUserHandle': body.response.userHandle,
+                    'webAuthnType': body.type
+                });
             })
             .catch(err => {
                 result.append("Login failed: " + err);
@@ -207,14 +249,13 @@
 
         webAuthn.registerOnly({name: userName, displayName: userName /*firstName + " " + lastName*/})
             .then(body => {
-                // store the registration JSON in form elements
-                fillOrHideFormField('webAuthnId', body.id);
-                fillOrHideFormField('webAuthnRawId', body.rawId);
-                fillOrHideFormField('webAuthnResponseAttestationObject', body.response.attestationObject);
-                fillOrHideFormField('webAuthnResponseClientDataJSON', body.response.clientDataJSON);
-                fillOrHideJsonField('webAuthnResponseClientDataJSONJson', body.response.clientDataJSON);
-                fillOrHideFormField('webAuthnType', body.type);
-
+                form("/webauthn/register", {
+                    'webAuthnId': body.id,
+                    'webAuthnRawId': body.rawId,
+                    'webAuthnResponseAttestationObject': body.response.attestationObject,
+                    'webAuthnResponseClientDataJSON': body.response.clientDataJSON,
+                    'webAuthnType': body.type
+                });
             })
             .catch(err => {
                 result.append("Registration failed: " + err);
diff --git a/src/main/resources/META-INF/resources/js/webauthn-debug.js b/src/main/resources/META-INF/resources/js/webauthn-debug.js
index 139815c..1a7428b 100644
--- a/src/main/resources/META-INF/resources/js/webauthn-debug.js
+++ b/src/main/resources/META-INF/resources/js/webauthn-debug.js
@@ -112,9 +112,23 @@
             return Promise.resolve(params);
         };
 
-        this._debugFetch = function (stage, input, init) {
-            return this.debuggingFunction(stage + "-request", {input: input, init: init})
-                .then(params => fetch(params.input, params.init))
+        this._debugPostJson = function (stage, url, body) {
+            return this.debuggingFunction(stage + "-request", {url: url, body: body})
+                .then(params => fetch(params.url, {
+                    method: 'POST',
+                    headers: {
+                        'Accept': 'application/json',
+                        'Content-Type': 'application/json'
+                    },
+                    body: JSON.stringify(params.body)
+                }))
+                .then(res => {
+                    if (res.status >= 200 && res.status < 300) {
+                        return res;
+                    }
+                    throw new Error(res.statusText);
+                })
+                .then(res => res.json())
                 .then(resp => this.debuggingFunction(stage + "-response", resp));
         }
 
@@ -134,21 +148,7 @@
         if (!self.registerPath) {
             return Promise.reject('Register path missing form the initial configuration!');
         }
-        return self._debugFetch("register", self.registerPath, {
-            method: 'POST',
-            headers: {
-                'Accept': 'application/json',
-                'Content-Type': 'application/json'
-            },
-            body: JSON.stringify(user || {})
-        })
-            .then(res => {
-                if (res.status === 200) {
-                    return res;
-                }
-                throw new Error(res.statusText);
-            })
-            .then(res => res.json())
+        return self._debugPostJson("register", self.registerPath, user || {})
             .then(res => {
                 res.challenge = base64ToBuffer(res.challenge);
                 res.user.id = base64ToBuffer(res.user.id);
@@ -159,8 +159,7 @@
                 }
                 return res;
             })
-            .then(res => self._debugAround("credentials-create", x => navigator.credentials.create(x), {publicKey: res}))
-            .then(credential => {
+            .then(res => self._debugAround("credentials-create", x => navigator.credentials.create(x).then(credential => {
                 return {
                     id: credential.id,
                     rawId: bufferToBase64(credential.rawId),
@@ -170,49 +169,22 @@
                     },
                     type: credential.type
                 };
-            });
+            }), {publicKey: res}));
+
     };
 
     WebAuthn.prototype.register = function (user) {
         const self = this;
         return self.registerOnly(user)
             .then(body => {
-                return self._debugFetch("register-callback", self.registerCallbackPath, {
-                    method: 'POST',
-                    headers: {
-                        'Accept': 'application/json',
-                        'Content-Type': 'application/json'
-                    },
-                    body: JSON.stringify(body)
-                })
-            })
-            .then(res => {
-                if (res.status >= 200 && res.status < 300) {
-                    return res;
-                }
-                throw new Error(res.statusText);
+                return self._debugPostJson("register-callback", self.registerCallbackPath, body)
             });
     };
 
     WebAuthn.prototype.login = function (user) {
         const self = this;
         return self.loginOnly(user)
-            .then(body => {
-                return self._debugFetch("login-callback", self.loginCallbackPath, {
-                    method: 'POST',
-                    headers: {
-                        'Accept': 'application/json',
-                        'Content-Type': 'application/json'
-                    },
-                    body: JSON.stringify(body),
-                })
-            })
-            .then(res => {
-                if (res.status >= 200 && res.status < 300) {
-                    return res;
-                }
-                throw new Error(res.statusText);
-            });
+            .then(body => self._debugPostJson("login-callback", self.loginCallbackPath, body))
     };
 
     WebAuthn.prototype.loginOnly = function (user) {
@@ -220,21 +192,7 @@
         if (!self.loginPath) {
             return Promise.reject('Login path missing from the initial configuration!');
         }
-        return self._debugFetch("login", self.loginPath, {
-            method: 'POST',
-            headers: {
-                'Accept': 'application/json',
-                'Content-Type': 'application/json'
-            },
-            body: JSON.stringify(user)
-        })
-            .then(res => {
-                if (res.status === 200) {
-                    return res;
-                }
-                throw new Error(res.statusText);
-            })
-            .then(res => res.json())
+        return self._debugPostJson("login", self.loginPath, user)
             .then(res => {
                 res.challenge = base64ToBuffer(res.challenge);
                 if (res.allowCredentials) {
@@ -244,8 +202,7 @@
                 }
                 return res;
             })
-            .then(res => self._debugAround("credentials-get", x => navigator.credentials.get(x), {publicKey: res}))
-            .then(credential => {
+            .then(res => self._debugAround("credentials-get", x => navigator.credentials.get(x).then(credential => {
                 return {
                     id: credential.id,
                     rawId: bufferToBase64(credential.rawId),
@@ -257,7 +214,8 @@
                     },
                     type: credential.type
                 };
-            })
+            }), {publicKey: res}))
+
     };
 
     return WebAuthn;