Artifactory supports NuGet repositories with Allow Anonymous Access enabled.
When Allow Anonymous Access is enabled, Artifactory will not query the NuGet client for authentication parameters by default, so you need to indicate to Artifactory to request authentication parameters differently.
You can override the default behavior by setting the Force Authentication checkbox in the New or Edit Repository dialog.
When set, Artifactory will first request authentication parameters from the NuGet client before trying to access this repository.