To ensure privacy over operator's private key, an alternative to write it down in the .env file would be to use Keystores as presented by Othentic in the following documentation:
//.env
...
WALLET_KEYSTORE_PATH=.keystore/c54b33db-311c-4e32-9ed3-375e5c0b6f0c # Keystore path
WALLET_KEYSTORE_PASSWORD=123
OPERATOR_ADDRESS=0xabc # Only include if Controller Key and Consensus Key differ