docs: add SESSION_SECRET_FILE and OAUTH_CLIENT_SECRET_FILE env vars

.env.example

@@ -48,6 +48,8 @@ JMAP_SERVER_URL=https://your-jmap-server.com
 
 # OAuth client secret (server-side only, never exposed to the browser)
 # OAUTH_CLIENT_SECRET=your-client-secret
+# Alternatively, you can specify the path to a file containing the OAuth client secret.
+# OAUTH_CLIENT_SECRET_FILE=/oauth-client-secret
 
 # OpenID Connect issuer URL for discovery
 # OAUTH_ISSUER_URL=https://your-idp.example.com
@@ -60,6 +62,8 @@ JMAP_SERVER_URL=https://your-jmap-server.com
 # Required for both "Remember me" and settings sync features.
 # Generate with: openssl rand -base64 32
 # SESSION_SECRET=your-secret-key-here
+# Alternatively, you can specify the path to a file containing the session secret.
+# SESSION_SECRET_FILE=/session-secret
 
 # =============================================================================
 # Settings Sync

README.md

@@ -271,6 +271,7 @@ PORT=3000            # Default listen port
 OAUTH_ENABLED=true
 OAUTH_CLIENT_ID=webmail
 OAUTH_CLIENT_SECRET=              # optional, for confidential clients
+OAUTH_CLIENT_SECRET_FILE=         # Path to a file containing the client secret
 OAUTH_ISSUER_URL=                 # optional, for external IdPs (Keycloak, Authentik)
 ```
 
@@ -282,7 +283,8 @@ Endpoints are auto-discovered via `.well-known/oauth-authorization-server` or `.
 <summary>Remember Me</summary>
 
 ```env
-SESSION_SECRET=your-secret-key    # Generate with: openssl rand -base64 32
+SESSION_SECRET=your-secret-key       # Generate with: openssl rand -base64 32
+SESSION_SECRET_FILE=/session-secret  # Path to a file containing the session secret
 ```
 
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