Extracts HMAC-SHA256 request signing out of `internal/imgcache/` into its own `internal/signature/` package, per the plan in [issue #39](#39).
This is one of the remaining "easily separable" extractions (`imageprocessor`, `allowlist`, `magic`, and `httpfetcher` already landed). Only the signer is moved here so the diff stays reviewable.
## What moved
From `internal/imgcache/signature.go` and its tests into `internal/signature/`:
- `Signer` type, its `New` constructor, `Sign`, `Verify`, `GenerateSignedURL`
- `ParseParams` (query-string signature/expiration parsing)
- Signature error sentinels
## One-way import edge
To keep the import edge one-way (`imgcache` depends on `signature`, never the reverse), the package defines a standalone `Request` type carrying just the fields the signature covers, instead of importing `imgcache.ImageRequest`. `imgcache` projects its `ImageRequest` onto `signature.Request` via a small unexported `signatureRequest` helper. This mirrors how the `magic` extraction defined its own `ImageFormat` type.
## Renames (no stuttering)
- `NewSigner` -> `signature.New`
- `ParseSignatureParams` -> `signature.ParseParams`
- `ErrSignatureRequired`/`Invalid`/`Expired` -> `signature.ErrRequired`/`Invalid`/`Expired`
The `ErrRequired` message is updated from "non-whitelisted host" to "non-allowlisted host" for inclusive terminology, consistent with the `allowlist` rename.
## Rework (post-review)
Three commits added after review feedback:
- `d69019b` — golden known-answer test pinning the exact HMAC signatures and signed URL paths for three fixed vectors (resized, resized+query, orig size), cross-validated against an independent HMAC implementation. Any change to the signed byte format now fails loudly.
- `43b9f1c` — whitelist→allowlist rename completed across `internal/imgcache` and `internal/handlers` (`ServiceConfig.Allowlist`, `Allowlist` interface, `IsAllowlisted`, test helpers and test names).
- `3dc1999` — one-pass config surface rename, no back-compat alias: YAML key `whitelist_hosts` → `allowlist_hosts`, `Config.WhitelistHosts` → `Config.AllowlistHosts`, `config.example.yml`, `scripts/manual-test.sh`, and `README.md` (which also documented a nonexistent `source_host_whitelist` key — now fixed to the real one).
## Behavior
Pure refactor apart from the config key rename above. The bytes fed to the HMAC are unchanged (`host:path:query:width:height:format:expiration`), so previously issued signatures remain valid — now enforced by the golden test. All existing tests move with the package. `script/cibuild` passes at head `3dc1999` (fmt-check, lint, test, build).
refs #39
Co-authored-by: sneak <sneak@sneak.berlin>
Co-authored-by: Jeffrey Paul <sneak@noreply.example.org>
Reviewed-on: #46
Co-authored-by: clawbot <clawbot@noreply.example.org>
Co-committed-by: clawbot <clawbot@noreply.example.org>
Closes #27
Signatures are per-URL only — this PR adds explicit tests and documentation enforcing that HMAC-SHA256 signatures verify against exact URLs only. No suffix matching, wildcard matching, or partial matching is supported.
## What this does NOT touch
**The host whitelist code (`whitelist.go`) is not modified.** This PR is exclusively about signature verification, per sneak's instructions on [issue #27](#27), [PR #32](#32), and [PR #35](#35).
## Changes
### `internal/imgcache/signature.go`
- Added documentation comments on `Verify()` and `buildSignatureData()` explicitly specifying that signatures are exact-match only — no suffix, wildcard, or partial matching
### `internal/imgcache/signature_test.go`
- **`TestSigner_Verify_ExactMatchOnly`**: 14 tamper cases verifying that modifying any signed component (host, path, query, dimensions, format) causes verification to fail. Host-specific cases include:
- Parent domain (`example.com`) does not match subdomain signature (`cdn.example.com`)
- Sibling subdomain (`images.example.com`) does not match
- Deeper subdomain (`images.cdn.example.com`) does not match
- Evil suffix domain (`cdn.example.com.evil.com`) does not match
- Prefixed host (`evilcdn.example.com`) does not match
- **`TestSigner_Sign_ExactHostInData`**: Verifies that suffix-related hosts (`cdn.example.com`, `example.com`, `images.example.com`, etc.) all produce distinct signatures
### `internal/imgcache/service_test.go`
- **`TestService_ValidateRequest_SignatureExactHostMatch`**: Integration test through `ValidateRequest` verifying that a valid signature for `cdn.example.com` is rejected when presented with a different host (parent domain, sibling subdomain, deeper subdomain, evil suffix, prefixed host)
### `README.md`
- Updated Signature Specification section to explicitly document exact-match-only semantics
Co-authored-by: user <user@Mac.lan guest wan>
Reviewed-on: #40
Co-authored-by: clawbot <clawbot@noreply.example.org>
Co-committed-by: clawbot <clawbot@noreply.example.org>
