"""
- Set environment variable
OAUTH2_SECRET_KEY
. - Send token in
Authorization: Bearer <token>
header.
- Send client certificate via
X-Client-Cert
header (for mock testing). - For production, integrate with mTLS.
- Set env
VALID_API_KEYS
(comma-separated keys). - Send
X-API-Key: <your_key>
in the header. """