Not shipping any implementation out of the box.

... because the fallback behaviour is sufficient for compatibility. In this way, we can phase in this feature more slowly

core/src/main/java/jenkins/security/DefaultProjectAuthenticator.java

-package jenkins.security;
-
-import hudson.Extension;
-import hudson.model.AbstractProject;
-import hudson.security.ACL;
-import org.acegisecurity.Authentication;
-import org.kohsuke.stapler.DataBoundConstructor;
-
-/**
- * @author Kohsuke Kawaguchi
- */
-public class DefaultProjectAuthenticator extends ProjectAuthenticator {
-    @DataBoundConstructor
-    public DefaultProjectAuthenticator() {
-    }
-
-    @Override
-    public Authentication authenticate(AbstractProject<?, ?> project) {
-        return ACL.SYSTEM;
-    }
-
-    @Extension
-    public static class DescriptorImpl extends ProjectAuthenticatorDescriptor {
-        @Override
-        public String getDisplayName() {
-            return "Default"; // TODO: fix
-        }
-    }
-}

core/src/main/resources/jenkins/security/ProjectAuthenticatorConfiguration/config.groovy

@@ -21,12 +21,16 @@
  * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
  * THE SOFTWARE.
  */
-package jenkins.security.ProjectAuthenticatorConfiguration;
+package jenkins.security.ProjectAuthenticatorConfiguration
+
+import jenkins.security.ProjectAuthenticatorDescriptor;
 
 f=namespace(lib.FormTagLib)
 
-f.section(title:_("Access Control for Builds")) {
-    f.block() {
-        f.repeatableHeteroProperty(field:"authenticators",hasHeader:true)
+if (!ProjectAuthenticatorDescriptor.all().isEmpty()) {
+    f.section(title:_("Access Control for Builds")) {
+        f.block() {
+            f.repeatableHeteroProperty(field:"authenticators",hasHeader:true)
+        }
     }
 }