Path to file which contains the master key. By doing so, all routes will be protected and will require a key to be accessed. If no master key is provided, all routes can be accessed without requiring any key.
You can generate a master key by running openssl rand -base64 36. Alternatively, you can start Meilisearch without a master key and use the pre-generated key from the service's logs that can be obtained by journalctl -u meilisearch | grep -- --master-key.