docs: update configuration to mention APP_SECRET_FILE

apps/docs/content/docs/configuration.mdx

@@ -12,12 +12,17 @@ Zerobyte is configured through environment variables and Docker Compose settings
 | Variable | Description | Example |
 |----------|-------------|---------|
 | `BASE_URL` | The URL where Zerobyte will be accessed. Controls cookie security and CORS behavior. | `http://localhost:4096` or `https://zerobyte.example.com` |
-| `APP_SECRET` | Random secret key (32+ characters) used to encrypt sensitive data in the database. Generate with `openssl rand -hex 32`. | `94bad46e...c66e25d5c2b` |
+| `APP_SECRET` | Random secret key (32+ characters) used to encrypt sensitive data in the database. Generate with `openssl rand -hex 32`. Set this or `APP_SECRET_FILE`, but not both. | `94bad46e...c66e25d5c2b` |
+| `APP_SECRET_FILE` | Alternative to `APP_SECRET`. Path to a file containing the app secret, useful with Docker or Kubernetes secrets. Set this or `APP_SECRET`, but not both. | `/run/secrets/app_secret` |
 
 <Callout type="warn">
   Never share or commit your `APP_SECRET`. If you lose it, encrypted data (credentials stored for volumes and repositories) cannot be recovered.
 </Callout>
 
+<Callout type="info">
+  Zerobyte reads the contents of `APP_SECRET_FILE`, trims surrounding whitespace and newlines, and applies the same 32-256 character requirement as `APP_SECRET`.
+</Callout>
+
 ### Recommended
 
 | Variable | Description | Default |
@@ -37,6 +42,33 @@ Zerobyte is configured through environment variables and Docker Compose settings
 | `RCLONE_CONFIG_DIR` | Path to the rclone config directory inside the container. | `/root/.config/rclone` |
 | `PROVISIONING_PATH` | Path to a JSON file with operator-managed repositories and volumes to sync at startup. | (none) |
 
+## Using APP_SECRET_FILE
+
+If you prefer not to place the app secret directly in `environment:`, mount it as a file and point `APP_SECRET_FILE` at that path.
+
+```yaml docker-compose.yml
+services:
+  zerobyte:
+    environment:
+      - BASE_URL=https://zerobyte.example.com
+      - APP_SECRET_FILE=/run/secrets/app_secret
+    secrets:
+      - app_secret
+
+secrets:
+  app_secret:
+    file: ./secrets/app_secret.txt
+```
+
+Generate the secret file with:
+
+```bash
+mkdir -p ./secrets
+openssl rand -hex 32 > ./secrets/app_secret.txt
+```
+
+Do not set `APP_SECRET` at the same time. Zerobyte will fail to start if both are configured.
+
 ## Docker Compose Settings
 
 ### Volume Mounts

apps/docs/content/docs/troubleshooting.mdx

@@ -27,9 +27,10 @@ docker logs -f zerobyte
 ## Container Won't Start
 
 1. Check logs: `docker compose logs zerobyte`
-2. Verify `APP_SECRET` is set and at least 32 characters
+2. Verify exactly one of `APP_SECRET` or `APP_SECRET_FILE` is set
-3. Ensure `/var/lib/zerobyte` exists and has correct permissions
+3. If using `APP_SECRET_FILE`, ensure the file exists inside the container, is readable, and contains a 32-256 character secret
-4. Verify port 4096 is not already in use: `netstat -tuln | grep 4096`
+4. Ensure `/var/lib/zerobyte` exists and has correct permissions
+5. Verify port 4096 is not already in use: `netstat -tuln | grep 4096`
 
 ### Permission Issues