feat: implement tenant OAuth flow and guest achievements

resources/js/admin/auth/utils.ts

@@ -0,0 +1,20 @@
+export function base64UrlEncode(buffer: Uint8Array): string {
+  let binary = '';
+  buffer.forEach((byte) => {
+    binary += String.fromCharCode(byte);
+  });
+  return btoa(binary).replace(/\+/g, '-').replace(/\//g, '_').replace(/=+$/g, '');
+}
+
+export function decodeStoredTokens<T>(value: string | null): T | null {
+  if (!value) {
+    return null;
+  }
+
+  try {
+    return JSON.parse(value) as T;
+  } catch (error) {
+    console.warn('[Auth] Failed to parse stored tokens', error);
+    return null;
+  }
+}