That is used by components like "NameNode", "SecondaryNameNode" , "MR2 History Server", "Oozie", "WebHCat" ...etc and other other components listed in the following doc to provide a secure http access to various HTTP based resources like UI.
- By default, access to the HTTP-based services and UI’s for the cluster are not configured to
require authentication. Kerberos authentication can be configured for the Web UIs for HDFS,
YARN, MapReduce2, HBase, Oozie, Falcon and Storm.
Following link provides more details about the same: