Visit my.sonatype.com for documentation on Nexus Repository version 2.
Currently authenticated access from yum to Nexus Repository 2 will not work due to this bug:
The python-urlgrabber library (which yum depends on) does not support http basic authentication.
You can work around this by applying the patch on the above issue to python-urlgrabber and setting up the yum/repos.d file like this (with credentials embedded into the URL):
But this has a very significant downside. Any yum command which prints the URLs will show the credentials. This likely includes yum commands which can be run by end users.
Consequentially, we really can't recommend doing this.
Update: RHEL 7 does not require the patch above, but still only supports URL encoded credentials.