Secret key used for signing data source settings like secrets and passwords. Set this to a unique, random string in production, generated for example by running openssl rand -hex 32.
If you change this later you will need to update data source settings to re-encode them.
https://grafana.com/docs/grafana/latest/setup-grafana/configure-grafana/#secret_key
Please note that the contents of this option will end up in a world-readable Nix store. Use the file provider pointing at a reasonably secured file in the local filesystem to work around that. Look at the documentation for details: https://grafana.com/docs/grafana/latest/setup-grafana/configure-grafana/#file-provider.