Replicates main.py's AuthMiddleware so /go/ can be exposed safely:
- internal-trust: private source IP AND no X-Forwarded-For => skip auth
(loopback/compose callers; nginx adds XFF to all internet traffic).
- session cookie: byte-compatible itsdangerous URLSafeTimedSerializer verify
(HMAC-SHA1, django-concat key derivation sha1("itsdangerous"+"signer"+key),
Unix-epoch timestamp, urlsafe-b64 no pad, optional zlib payload), keyed on the
same SECRET_KEY. 30-day max-age. Public allowlist (/login,/logout,login assets,
/icons/,/health); 302->/login for html, 401 JSON otherwise.
Validated on the server: internal-trust loopback 200; external no-cookie 401;
html 302; valid cookie 200; tampered 401; /health public 200; and the SAME
Python-issued cookie authenticates BOTH services (cross-compat proof).
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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