I’m currently working on a very basic demo with the Rancher API. The documentation for the specific endpoint to change a user password is a little bare. The example explorer does not show a field for the actual user you want to change the password of.
The changepassword action is for the user who is logged in and making the request, and requires knowing their current password. This is the self-service “change my password” flow. It’s on the collection (instead of an individual /v3/users/<id>) because the person who’s logged in doesn’t necessarily have access to list users and find themselves in the collection.
If you are logged in as an admin, then individual /v3/user entries also have a setpassword action which will let you just set a new password for them (without knowing the old one). This is more like an help desk ticket “Steve forgot his password, can you help him” flow.