When "Require user tokens for repository authentication" is set nexus does not send an authorization header

Configure user token access in the server, and enable "Require user tokens for repository authentication".  Then run a Maven build against the server.  Artifact downloads will fail with 401 even if a valid token is used.

The reason for this is that Maven by default sends requests with non-preemptive authentication, and will only send credentials in response to a 401 response with a challenge header.  The challenge header is missing in the response.  Nexus should be setting something like:

WWW-Authenticate: BASIC realm="Sonatype Nexus Repository Manager"