File README.security of Package etcd

By default etcd doesn't require authentication. If you configure etcd to be reachable
over the network, have untrustworthy local users on the system where etc runs or store
data in etcd that needs to be kept confidential please make sure to enable authentication.

You can do that by configuring the settings under the Security section in /etc/default/etcd.

For additional guidance please read:
https://etcd.io/docs/v3.6/op-guide/configuration/#security

And to ensure that you enforce proper access control:
https://etcd.io/docs/v3.6/op-guide/authentication/