AuthToken needed even in non-https mode in 3.2.16

[sttts]

Compare kubernetes/kubernetes#60299.

Without setting AuthToken in the server config struct, one gets:

utils.go:293: Failed to start etcd server error=failed to initialize the etcd server: auth: invalid auth options

Is this intentional?

[mitake]

@sttts thanks for your report. Probably allowing empty AuthToken would be rationale. How do you think? @xiang90 If it is ok, I'll work on it.

[gyuho]

@mitake How about default to "simple" in etcdserver.NewServer, rather than implementing no-op TokenProvider with empty token?

[mitake]

@gyuho probably providing a nop auth token provider would be valuable because the stateful nature of simple token provides complexity and the jwt token requires keys for signing and verifying even if it isn't used. The nop token provider will be useful for deployments where CN based authentication is used.