seal.DeriveKeys derives the session hash and block keys, the encrypted URL
key and the CSRF key from the signing key, with their salts declared beside
it, and returns them as one seal.Keys. internal/providers calls it once at
startup and provides the value to the fx graph. The session manager, the
encrypted URL generator and the CSRF protection each take their own key.
session.NewManager, encurl.NewGenerator, newCSRFProtect and handlers.New
return no error, as nothing in them can fail now. Each key is derived as
before, with seal.DeriveKey and the same salt. The signing key itself stays
the HMAC key of signed URLs and the login password. README.md says under
signing_key what it protects.
Model: opus-5-5
Adds CSRF protection to the two cookie-authenticated form posts, POST / (login) and POST /generate, using github.com/gorilla/csrf, the recorded default for this job.
The token key is derived from signing_key with its own HKDF salt, so it needs no new config and survives restarts. The token cookie is separate from the session cookie, which also covers login CSRF, where no session exists yet. Both templates carry the hidden token field.
What a reader would trip over: outside debug mode the library enforces its https Referer origin check, so the TLS-terminating proxy must preserve the Host and Referer headers from the browser or form posts are rejected.
Disclosure: one nolint:gosec on a test constant holding the library field name (G101 false positive).
Model: opus-4-8 (implementation, review); fable-5-1 (landing message)
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