• OIDC login uses Authorization Code + PKCE.
• ID token is validated against provider JWKS.
• Mailbox password is never stored plaintext.
• Decryption occurs only at runtime for auth/connect operations.
• Audit records are stored for key auth/provisioning events.

Default mode (zero-knowledge disabled):

• Passwords are encrypted at rest with server-side key material.
• Preferred algorithm: libsodium sodium_secretbox.
• Fallback: AES-256-GCM via OpenSSL.
• Key source: RCUBE_MAILBOX_KEY / RCUBE_MAILBOX_KEYS.

Zero-knowledge mode (client-side enabled):

• Browser wraps mailbox secret using passphrase-derived key before submit.
• Server stores wrapped blob and metadata.
• User unlocks post-OIDC with passphrase.

• Enforce HTTPS end-to-end.
• Keep secrets in environment or secret manager.
• Rotate keyring safely with RCUBE_MAILBOX_KEYS + rotate script.
• Keep strict mailbox binding (ALLOW_CUSTOM_MAILBOX_EMAIL=false) unless explicitly needed.
• Keep standard login disabled (DISABLE_PASSWORD_LOGIN=true) for OIDC-only posture.

add_header Strict-Transport-Security "max-age=31536000; includeSubDomains" always;
add_header X-Frame-Options "SAMEORIGIN" always;
add_header X-Content-Type-Options "nosniff" always;
add_header Referrer-Policy "strict-origin-when-cross-origin" always;
add_header Content-Security-Policy "default-src 'self'; img-src 'self' data: https:; style-src 'self' 'unsafe-inline' https://cdn.jsdelivr.net; script-src 'self'; connect-src 'self'; frame-ancestors 'self';" always;

Header always set Strict-Transport-Security "max-age=31536000; includeSubDomains"
Header always set X-Frame-Options "SAMEORIGIN"
Header always set X-Content-Type-Options "nosniff"
Header always set Referrer-Policy "strict-origin-when-cross-origin"
Header always set Content-Security-Policy "default-src 'self'; img-src 'self' data: https:; style-src 'self' 'unsafe-inline' https://cdn.jsdelivr.net; script-src 'self'; connect-src 'self'; frame-ancestors 'self';"