nx_basic_auth.nx

basic_auth.nx -- HTTP Basic Authentication (RFC 7617). Authorization header format: Authorization: Basic BASE64(username:password) The oldest HTTP auth scheme. Still everywhere: admin-panel login, IoT device configs, CI runner tokens, registry push, htpasswd-protected directories, internal tools. Combined with HTTPS it's adequate; on plain HTTP it's trivially sniffable. We ship encoder + decoder + Authorization-header matcher. Composes base64.nx. Invariants: BA1 Encoded output is \"Basic \" + base64(\"user:pass\"), one ASCII line. BA2 Decoder strips the leading \"Basic \" prefix case- insensitively per RFC 7617 §2. BA3 username + password round-trip byte-exact. BA4 Compare uses constant-time memcmp via ct.nx for the password half -- timing attacks on admin logins are real.