diff --git a/.jules/sentinel.md b/.jules/sentinel.md
index 518c5af..a847428 100644
--- a/.jules/sentinel.md
+++ b/.jules/sentinel.md
@@ -9,3 +9,16 @@ Always use an environment variable (like `ALLOWED_ORIGINS`) to strictly define a
 **Prevention:**
 1. Do not use wildcard `["*"]` for CORS in production setups, especially with authenticated routes.
 2. Verify CORS setups using testing frameworks like Pytest or by configuring restricted inputs dynamically through the `.env` configuration.
+
+## 2024-05-18 - Hardcoded Admin Credentials Vulnerability
+
+**Vulnerability:**
+The `backend/auth.py` file contained hardcoded admin credentials (`username != "admin"` or `password != "admin123"`) directly in the source code. This is a critical security vulnerability that exposes administrative access to anyone who can read the repository. Furthermore, the standard string comparison `!=` is vulnerable to timing attacks.
+
+**Learning:**
+Hardcoded credentials are a common but severe risk, especially in initial project templates. Authentication checks should never use simple string comparisons, as it allows attackers to guess valid credentials character-by-character based on response time.
+
+**Prevention:**
+1. Always store sensitive credentials (like passwords, API keys, admin usernames) in environment variables or a secure vault, never in source code.
+2. Use `secrets.compare_digest(a.encode('utf-8'), b.encode('utf-8'))` for comparing sensitive strings to prevent timing attacks, and always encode to avoid TypeErrors with non-ASCII characters.
+3. Fail securely by raising a 500 error if required authentication configuration (like environment variables) is missing, rather than defaulting to an insecure state.
diff --git a/backend/auth.py b/backend/auth.py
index 1f396ff..2347e3b 100644
--- a/backend/auth.py
+++ b/backend/auth.py
@@ -1,7 +1,18 @@
+import os
+import secrets
 from fastapi import HTTPException
 
 def authenticate_admin(username: str, password: str):
-    # Dummy authentication logic
-    if username != "admin" or password != "admin123":
+    admin_username = os.environ.get("ADMIN_USERNAME")
+    admin_password = os.environ.get("ADMIN_PASSWORD")
+
+    if not admin_username or not admin_password:
+        raise HTTPException(status_code=500, detail="Admin credentials are not configured on the server.")
+
+    is_username_correct = secrets.compare_digest(username.encode('utf-8'), admin_username.encode('utf-8'))
+    is_password_correct = secrets.compare_digest(password.encode('utf-8'), admin_password.encode('utf-8'))
+
+    if not (is_username_correct and is_password_correct):
         raise HTTPException(status_code=401, detail="Invalid username or password")
+
     return {"message": "Login successful"}