Thanks for the explanation Andrew Wang! Sorry I didn't ask the correct question.
On KMS documentation page, it first explains KMS delegation token configuration, then talks about HA in another section, where it's called 'Using Multiple Instances of KMS Behind a Load-Balancer or VIP'.
Since authentication is done by KMSAuthenticationFilter, which inherits from DelegationTokenAuthenticationFilter which inherits from AuthenticationFilter, I think from configuration and example point of view, they're the same as those given in 'HTTP Authentication Signature' in the same KMS HA section.
I also found that the Hadoop Auth page describes about the signer in details, and the last example being configuring multiple ZKs (here).
So I'm thinking of just add some descriptive text on the delegation tokens HA section, and point to the Auth page. (Auth page seems a bit out dated, will modify as well.) One confusion though is the xml format is different, but I think that can be easily explained, and better than having 2 places showing similar examples. Does this sound right to you? Please correct me if I misunderstood anything.