feat: add Docker _FILE secret convention for sensitive env vars (#205)

Support reading secrets from mounted files instead of plain-text
environment variables, following the standard Docker/Kubernetes
convention used by MariaDB, Postgres, and Stirling-PDF.

Supported vars: DEFAULT_PASSWORD, S3_ACCESS_KEY_ID,
S3_SECRET_ACCESS_KEY, OIDC_CLIENT_SECRET, COOKIE_SECRET,
SNAPOTTER_LICENSE_KEY.

docker/docker-compose-gpu.yml

@@ -51,6 +51,15 @@ services:
       # - OIDC_USERNAME_CLAIM=preferred_username
       # - OIDC_CLOCK_TOLERANCE=30
       # - COOKIE_SECRET=
+      #
+      # Docker secrets (_FILE convention): mount secrets as files instead of
+      # passing them as plain-text env vars. Supported for sensitive vars only.
+      # - DEFAULT_PASSWORD_FILE=/run/secrets/snapotter_password
+      # - S3_ACCESS_KEY_ID_FILE=/run/secrets/s3_access_key
+      # - S3_SECRET_ACCESS_KEY_FILE=/run/secrets/s3_secret_key
+      # - OIDC_CLIENT_SECRET_FILE=/run/secrets/oidc_secret
+      # - COOKIE_SECRET_FILE=/run/secrets/cookie_secret
+      # - SNAPOTTER_LICENSE_KEY_FILE=/run/secrets/license_key
     restart: unless-stopped
     # --- Security hardening ---
     mem_limit: 8g
@@ -91,6 +100,13 @@ services:
         max-size: "50m"
         max-file: "5"
 
+# Uncomment to use Docker secrets (requires Docker Swarm or compose v2.23+):
+# secrets:
+#   snapotter_password:
+#     file: ./secrets/snapotter_password.txt
+#   oidc_secret:
+#     file: ./secrets/oidc_secret.txt
+
 volumes:
   SnapOtter-data:
   SnapOtter-workspace:

docker/docker-compose.yml

@@ -50,6 +50,15 @@ services:
       # - OIDC_USERNAME_CLAIM=preferred_username
       # - OIDC_CLOCK_TOLERANCE=30
       # - COOKIE_SECRET=
+      #
+      # Docker secrets (_FILE convention): mount secrets as files instead of
+      # passing them as plain-text env vars. Supported for sensitive vars only.
+      # - DEFAULT_PASSWORD_FILE=/run/secrets/snapotter_password
+      # - S3_ACCESS_KEY_ID_FILE=/run/secrets/s3_access_key
+      # - S3_SECRET_ACCESS_KEY_FILE=/run/secrets/s3_secret_key
+      # - OIDC_CLIENT_SECRET_FILE=/run/secrets/oidc_secret
+      # - COOKIE_SECRET_FILE=/run/secrets/cookie_secret
+      # - SNAPOTTER_LICENSE_KEY_FILE=/run/secrets/license_key
     restart: unless-stopped
     # --- Security hardening ---
     mem_limit: 6g
@@ -83,6 +92,13 @@ services:
         max-size: "50m"
         max-file: "5"
 
+# Uncomment to use Docker secrets (requires Docker Swarm or compose v2.23+):
+# secrets:
+#   snapotter_password:
+#     file: ./secrets/snapotter_password.txt
+#   oidc_secret:
+#     file: ./secrets/oidc_secret.txt
+
 volumes:
   SnapOtter-data:
   SnapOtter-workspace:

docker/entrypoint.sh

@@ -1,6 +1,44 @@
 #!/bin/sh
 set -e
 
+# --- Docker secret file convention (_FILE suffix) ---
+# For each supported var, if VAR_FILE is set, read the secret from that file
+# path into VAR. This lets users mount Docker/Kubernetes secrets instead of
+# passing credentials as plain-text environment variables.
+#
+# Supported: DEFAULT_PASSWORD, S3_ACCESS_KEY_ID, S3_SECRET_ACCESS_KEY,
+#            OIDC_CLIENT_SECRET, COOKIE_SECRET, SNAPOTTER_LICENSE_KEY
+resolve_file_env() {
+  var="$1"
+  file_var="${var}_FILE"
+  eval current_val="\"\${${var}:-}\""
+  eval file_path="\"\${${file_var}:-}\""
+
+  if [ -z "$file_path" ]; then
+    return
+  fi
+
+  if [ -n "$current_val" ]; then
+    echo "WARNING: Both $var and $file_var are set. $file_var takes precedence." >&2
+  fi
+
+  if [ ! -f "$file_path" ] || [ ! -r "$file_path" ]; then
+    echo "ERROR: $file_var points to '$file_path' but the file does not exist or is not readable." >&2
+    exit 1
+  fi
+
+  # Command substitution strips trailing newlines (standard for secret files)
+  export "$var"="$(cat "$file_path")"
+  unset "$file_var"
+}
+
+resolve_file_env DEFAULT_PASSWORD
+resolve_file_env S3_ACCESS_KEY_ID
+resolve_file_env S3_SECRET_ACCESS_KEY
+resolve_file_env OIDC_CLIENT_SECRET
+resolve_file_env COOKIE_SECRET
+resolve_file_env SNAPOTTER_LICENSE_KEY
+
 # Apply auth defaults at runtime so they are never baked into image layers.
 # Users can override any of these via -e flags at docker run time.
 export AUTH_ENABLED="${AUTH_ENABLED:-true}"