Add is-jwt util

src/utils/is-jwt.ts

@@ -0,0 +1,31 @@
+import atob from 'atob';
+
+/**
+ * Check if a given string conforms to the structure of a JWT.
+ */
+export default function isJWT(string: string) {
+	const parts = string.split('.');
+
+	// JWTs have the structure header.payload.signature
+	if (parts.length !== 3) return false;
+
+	// Check if all segments are base64 encoded
+	try {
+		atob(parts[0]);
+		atob(parts[1]);
+		atob(parts[2]);
+	} catch (err) {
+		console.log(err);
+		return false;
+	}
+
+	// Check if the header and payload are valid JSON
+	try {
+		JSON.parse(atob(parts[0]));
+		JSON.parse(atob(parts[1]));
+	} catch {
+		return false;
+	}
+
+	return true;
+}