Increment 2 - Step 2: Auth module

[angelobarbu]

Increment 2 – Step 2: Auth module

The cryptographic and data-access layer for authentication: password hashing, session tokens, the role catalogue, and the repositories that persist users and sessions - built on a new libpqxx connection pool.

What's new

• server/modules/auth (modulo_server_auth):
  • PasswordHasher - Argon2id via libsodium (crypto_pwhash_str): hash, constant-time verify, rehash detection. Cost profile is libsodium's INTERACTIVE (64 MiB, 2 passes) - above the OWASP Argon2id minimum at ~0.1 s per hash.
  • token - opaque session tokens: 32 CSPRNG bytes (libsodium) as unpadded base64url, and the SHA-256 digest (QCryptographicHash) that is the only form ever stored or compared.
  • Role - the fixed admin/user catalogue pinned to the schema ids, with name and id conversions.
  • UserRepository and SessionRepository - every method runs one transaction on a pooled connection and returns Result, never throws. A module-private pg.h owns the Qt-to-libpqxx boundary: string and bytea conversion, ISO-8601-in / epoch-milliseconds-out timestamps, and the mapping of libpqxx exceptions to stable db.* codes (auth.email_taken, auth.session_not_found layered on top).
• ConnectionPool in server/modules/db (Qt-free): lazy connection opening, RAII leases, blocks when exhausted, discards broken connections.
• core::validatePassword - the shared password rule (10 to 128 characters) the client will reuse for form validation.

Tests (5 new binaries)

• Unit: hasher (round trip, unique salts, unicode, malformed hashes, rehash), token (format, uniqueness, known-answer SHA-256), roles, password policy.
• Integration (modulo_auth_repositories_tests, opt-in via MODULO_TEST_DB_URL): pool reuse, case-insensitive email lookup, auth.email_taken with rollback, full session lifecycle, expiry, revoke-all scoping.

Notes

• libpqxx 8 specifics handled: result[i] is a row_ref (use one_row()), pqxx::bytes is std::vector<std::byte>.
• pg.h stays private to the auth module by design; it becomes a shared persistence module when the transactions module needs it in Increment 3.

Verified: ctest --preset all 12/12 with the database (integration suites report Skipped without it), clean -Werror build, format.sh --check green.