Hi,
This is unrelated to REST or to any specific API.
On NSO local-install, an 'admin' user is created by default with 'admin' password.
This user can be used out of the box on local-installs through any API (not just REST).
This is not the case for system-install, where user admin is not present by default.
If you want to change the password of user admin, you can modify this user's settings under 'aaa authentication users user admin'.
In system-install the story is a bit different and depends on whether you use local-authentication, PAM, remote-authentication or some of them or all of them.
If you use plain local auth, then the procedure will be the same as for local-install.
