feat(kms): sign & verify data

frontend/src/lib/fn/base64.ts

@@ -0,0 +1,14 @@
+const base64WithPadding =
+  /^(?:[A-Za-z0-9+/]{4})*(?:[A-Za-z0-9+/]{2}==|[A-Za-z0-9+/]{3}=|[A-Za-z0-9+/]{4})$/;
+
+export const isBase64 = (str: string): boolean => {
+  if (typeof str !== "string") {
+    throw new TypeError("Expected a string");
+  }
+
+  if (str === "") return true;
+
+  const regex = base64WithPadding;
+
+  return regex.test(str);
+};