fix: improve behavior when preferredToken=webAuthn in unsupported browser

switch method to OTP only once

www/js/loginform.js

@@ -60,6 +60,14 @@ function changeMode(newMode) {
   document.forms["piLoginForm"].submit();
 }
 
+function fallbackToOTP() {
+  if (value("mode") !== "otp") {
+    setTimeout(() => {
+      changeMode("otp");
+    }, 3000);
+  }
+}
+
 function setMessage(newMessage) {
   getElement("message").innerText = newMessage;
 }
@@ -113,14 +121,14 @@ function doWebAuthn() {
     console.log(
       "Insecure context detected: Aborting Web Authn authentication!"
     );
-    changeMode("otp");
+    fallbackToOTP();
     return;
   }
 
   if (!window.pi_webauthn) {
     enable("useWebAuthnButton");
     setMessage(t("webauthn_library_unavailable"));
-    changeMode("otp");
+    fallbackToOTP();
     return;
   }
 
@@ -163,7 +171,7 @@ function doU2F() {
   if (!window.isSecureContext) {
     setMessage(t("u2f_insecure_context"));
     console.log("Insecure context detected: Aborting U2F authentication!");
-    changeMode("otp");
+    fallbackToOTP();
     return;
   }
 
@@ -171,7 +179,7 @@ function doU2F() {
 
   if (requestStr === null) {
     setMessage(t("u2f_unavailable"));
-    changeMode("otp");
+    fallbackToOTP();
     return;
   }