diff --git a/src/js/common_webauthn.js b/src/js/common_webauthn.js
new file mode 100644
index 0000000..fa95364
--- /dev/null
+++ b/src/js/common_webauthn.js
@@ -0,0 +1,44 @@
+/**
+ * convert RFC 1342-like base64 strings to array buffer
+ * @param {mixed} obj
+ * @returns {undefined}
+ */
+function recursiveBase64StrToArrayBuffer(obj) {
+    let prefix = '=?BINARY?B?';
+    let suffix = '?=';
+    if (typeof obj === 'object') {
+        for (let key in obj) {
+            if (typeof obj[key] === 'string') {
+                let str = obj[key];
+                if (str.substring(0, prefix.length) === prefix && str.substring(str.length - suffix.length) === suffix) {
+                    str = str.substring(prefix.length, str.length - suffix.length);
+
+                    let binary_string = window.atob(str);
+                    let len = binary_string.length;
+                    let bytes = new Uint8Array(len);
+                    for (var i = 0; i < len; i++)        {
+                        bytes[i] = binary_string.charCodeAt(i);
+                    }
+                    obj[key] = bytes.buffer;
+                }
+            } else {
+                recursiveBase64StrToArrayBuffer(obj[key]);
+            }
+        }
+    }
+}
+
+/**
+ * Convert a ArrayBuffer to Base64
+ * @param {ArrayBuffer} buffer
+ * @returns {String}
+ */
+function arrayBufferToBase64(buffer) {
+    var binary = '';
+    var bytes = new Uint8Array(buffer);
+    var len = bytes.byteLength;
+    for (var i = 0; i < len; i++) {
+        binary += String.fromCharCode( bytes[ i ] );
+    }
+    return window.btoa(binary);
+}