🛡️ Sentinel: [CRITICAL] Fix Timing Attack in Bearer Token Validation

[google-labs-jules]

🚨 Severity: CRITICAL
💡 Vulnerability: The authentication middleware short-circuited token comparisons by checking length before calling crypto.timingSafeEqual, which leaks the length of the valid token.
🎯 Impact: Attackers can incrementally guess the token length by measuring response times, significantly reducing the search space to brute-force the actual token.
🔧 Fix: Hashed both the provided token and the configured authentication token to a fixed-length digest (SHA-256) before comparison, ensuring constant-time evaluation regardless of the input length.
✅ Verification: Ran unit and integration tests successfully.

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PR created automatically by Jules for task 8397989675660668138 started by @YoungSx

[google-labs-jules]

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