[Bug] - Inaccurate or unclear error messages if trying to create users or change bucket owners without IAM

[lrm25]

Describe the bug If versitygw is started without IAM, and the user attempts to change the bucket owner to the root account, the following error is returned:

user specified as the new bucket owner does not exist

This error is incorrect. Also, when attempting to create a user:

failed to create user: method is not supported

This is more correct, but confusing. There should probably be more info as to why the method isn't supported (in this case, versitygw being started without IAM).

To Reproduce

1. Start versitygw without IAM, e.g.: ROOT_ACCESS_KEY=<key> ROOT_SECRET_KEY=<key> ./versitygw --cert $PWD/cert.pem --key $PWD/versitygw.pem posix /tmp/gw

Expected behavior Accurate and clear error messages.

Server Version Version : v1.0.7 Build : b7291c3 BuildTime: 2024-09-25_08:28:23PM Darwin Lukes-MacBook-Pro.local 23.4.0 Darwin Kernel Version 23.4.0: Fri Mar 15 00:12:25 PDT 2024; root:xnu-10063.101.17~1/RELEASE_ARM64_T6030 arm64