Define cpu_alert demo occurs an error: unable to parse authentication credentials

I Installed Kapacitor1.6 with docker, but when i run a command from official documents:
kapacitor define cpu_alert -tick cpu_alert.tick
It occurs an error:
unable to parse authentication credentials
Why ?

Start with the Docker installation context and the official `kapacitor define cpu_alert -tick cpu_alert.tick` command, then inspect how authentication is configured for that container. Done means identifying the credential mismatch or missing configuration and confirming that the cpu_alert definition succeeds.

Written by the indexing model from the issue text.