session_id.nx

session_id.nx -- cryptographically strong session identifiers. Session IDs are the primary auth artefact after login. They must be: - Unpredictable (>= 128 bits entropy) - URL + cookie-safe characters - Fixed length (makes brute-force scans inherently bounded) - Cheap to validate format before DB lookup This module generates 32-char session IDs = 192 bits entropy over the URL-safe alphabet (A-Z a-z 0-9 - _). Matches the security profile of Django / Rails / Express session IDs. Composes rand.nx. Invariants: SI1 Every char from the 64-char URL-safe alphabet. SI2 Length fixed at 32 (customisable via session_id_with_len). SI3 Format-validation helper so callers can reject malformed IDs before DB lookup.