🔒 fix: use timing-safe comparison for webhook authentication

[Sparkier]

🎯 What: Fixed a timing attack vulnerability in webhook authentication checks by replacing the standard inequality operator (!==) with a timing-safe string comparison function (timingSafeEqual from node:crypto).

⚠️ Risk: The previous implementation used standard string comparison to verify the Authorization header against secret keys. Standard string comparison returns false as soon as it encounters a mismatched character. An attacker could exploit this by repeatedly sending requests with slightly different tokens and measuring the response time. By observing which character guesses take slightly longer (because they match and the comparison proceeds to the next character), they could theoretically deduce the secret key character by character, leading to unauthorized access to the webhooks.

🛡️ Solution:

• Added a safeCompare utility function in src/lib/utils.ts that safely handles string length differences and null values, and uses node:crypto's timingSafeEqual to perform the actual comparison in constant time.
• Updated the authentication checks in src/routes/api/newsletter/daily-digest/+server.ts, src/routes/api/webhooks/post/+server.ts, and src/routes/api/webhooks/google-sheets/+server.ts to use this new safeCompare function.
• This ensures that the time it takes to compare the tokens is independent of how many characters match, mitigating the timing attack vulnerability while maintaining functional equivalence.

📊 Coverage: All existing test suites pass.
✨ Result: Webhook endpoints are now secure against timing attacks.

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PR created automatically by Jules for task 7334669684848365334 started by @Sparkier

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Project	Deployment	Actions	Updated (UTC)
vis-positions	Canceled		Aug 1, 2026 11:29am

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