Credentials defined at a global scope work normally for the plugin when used inside of a job but when you move those credentials to be within a folder, the plugin will try to authenticate you as "null" which would indicate it can not find or use the credentials.

Working Scenario:

-Define your repository credentials at the Root Jenkins level

-Define a job which uses the Maven Artifact Choice List Provider plugin to connect to a repository requiring credentials to login

-Hit the "List Files Now" button and see it will connect without issue

Steps to reproduce the defect:

-Define a folder named "Folder Test"

-Define the same repository credentials at the folder level(different description from above)

-Create a new job within that Folder using the same Maven Artifact Choice List Provider plugin connection

-Hit the "List Files Now" and observe that a connection can not be made.

If you look at the logs of the defect, it appears to connect you anonymously to the repository