🛡️ Sentinel: [CRITICAL] Fix hardcoded admin credentials and exception leakage

[shadowcoder8]

🚨 Severity: CRITICAL
💡 Vulnerability: The authenticate_admin function used hardcoded credentials (admin/admin123) and a non-constant time comparison operator (!=), exposing secrets in version control and creating a timing attack vulnerability. The admin_login route in main.py leaked internal error details in its HTTPException message when an unexpected error occurred.
🎯 Impact: Attackers could easily compromise the admin account by reading the source code, or theoretically brute force passwords via timing attacks. Malicious actors could also gather internal system information if unexpected exceptions occurred during login.
🔧 Fix: Removed hardcoded credentials and implemented authentication using secrets.compare_digest with environment variables (ADMIN_USERNAME and ADMIN_PASSWORD). Updated exception handling in main.py to ensure only generic error messages are returned on unexpected faults, while explicitly allowing HTTPExceptions to pass through correctly.
✅ Verification: Tested via a custom automated script verifying that missing configs throw a 500, incorrect details throw a 401, and correct details pass. All existing tests were run and passed.

---

PR created automatically by Jules for task 2644715687232285276 started by @shadowcoder8

[google-labs-jules]

👋 Jules, reporting for duty! I'm here to lend a hand with this pull request.

When you start a review, I'll add a 👀 emoji to each comment to let you know I've read it. I'll focus on feedback directed at me and will do my best to stay out of conversations between you and other bots or reviewers to keep the noise down.

I'll push a commit with your requested changes shortly after. Please note there might be a delay between these steps, but rest assured I'm on the job!

For more direct control, you can switch me to Reactive Mode. When this mode is on, I will only act on comments where you specifically mention me with @jules. You can find this option in the Pull Request section of your global Jules UI settings. You can always switch back!

New to Jules? Learn more at jules.google/docs.

---

For security, I will only act on instructions from the user who triggered this task.