In the Maven Settings shown in Configuring Deployment Credentials for Nexus Site Deployment, you
configured your Maven instance to use the default deployment user and
password. To successfully deploy a site to Nexus,
make sure that the deployment user has the appropriate role and
permissions. To add the site deployment role to the deployment user,
click on Users under the Security section of the Nexus menu, and click
on the Add button in the Role Management section. This will trigger the
display of the Add Roles dialog that will allow you to apply a filter
site to locate the applicable roles as shown in Figure 20.4, “Adding the Site Deployment Role to the Deployment User”.
Check the box beside the "Repo: All Site Repositories (Full Control)" role in the list and press OK in the dialog. After the dialog closes, you should see the new role in the Role Management section. Click on the Save button to update the roles for the deployment user. The deployment user now has the ability to publish sites to a Maven site repository.