internal: add tests for LoggableHTTPHeader redaction

[Bojun-Vvibe]

Repo: caddyserver/caddy (⭐ 60000)
Type: test
Files changed: 1
Lines: +90/-0

What

Adds unit tests for internal.LoggableHTTPHeader.MarshalLogObject, covering: redaction of sensitive headers (Authorization, Proxy-Authorization, Cookie, Set-Cookie), pass-through of non-sensitive headers, opt-in credential logging via ShouldLogCredentials, case-insensitive header matching, and the nil-header no-op path.

Why

LoggableHTTPHeader guards against credential leakage in logs (see #5669, and the recent header redaction work in #7578), but the package had no tests covering the redaction behavior. Regressions here leak secrets into logs, so the behavior deserves explicit coverage. The internal package had no test file before this change.

Testing

go test ./internal/ passes locally (ok github.com/caddyserver/caddy/v2/internal 0.382s). Tests use zapcore.NewMapObjectEncoder — no new dependencies.

Risk

Low — test-only change in an internal package, no production code modified.

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