Andrey Antukh 64fe8e57e3 🐛 Fix SNS signature verification field sets per AWS spec
V1 and V2 use the same field sets (only hash algorithm differs).
The AWS documentation explicitly shows that SigningCertURL and
SignatureVersion are metadata fields, not part of the signed content.

Changes:
- Remove V2-specific field lists (SigningCertURL, SignatureVersion)
- Simplify build-string-to-sign to use unified field sets
- Fix resource leak in fetch-certificate (close stream on non-200)
- Fix missing Message field returning 200 instead of 400
- Stub fetch-certificate in network-dependent test
- Update V2 test to reflect correct field sets

Reference: https://docs.aws.amazon.com/sns/latest/dg/sns-verify-signature-of-message-verify-message-signature.html

AI-assisted-by: qwen3.7-plus
2026-08-05 18:22:19 +00:00
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