On the documentation for the the automationConfig resource for Ops Manager public API, the entries for auth.usersWanted.pwd and auth.usersWanted.initPwd imply that you can set the password for a user by setting either attribute. This is not true. If pwd is set, but the value does not match the hashed password for the user in the automationConfig currently, the API call will fail with:

HTTP/1.1 400 Bad Request
Date: Fri, 08 Dec 2017 19:32:40 GMT
Vary: Accept-Encoding
Content-Length: 176
Content-Type: application/json

{"detail":"Invalid automation config: The required attribute auth.usersWanted.initPwd was not specified.","error":400,"errorCode":null,"parameters":null,"reason":"Bad Request"}

The documentation just says to use one or the other, it does not point out that if the password is already set and you are trying to change it you must use initPwd. The entries for these two attributes on the page above should be updated to reflect this.