HDFS-7546. Document, and set an accepting default for dfs.namenode.kerberos.principal.pattern (Harsh J via aw)

(cherry picked from commit 63613c79c1)

hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt

@@ -316,6 +316,9 @@ Release 2.8.0 - UNRELEASED
     do not generate spurious reconfig warnings (Lei (Eddy) Xu via Colin P.
     McCabe)
 
+    HDFS-7546. Document, and set an accepting default for
+    dfs.namenode.kerberos.principal.pattern (Harsh J via aw)
+
   OPTIMIZATIONS
 
     HDFS-8026. Trace FSOutputSummer#writeChecksumChunks rather than

hadoop-hdfs-project/hadoop-hdfs/src/main/resources/hdfs-default.xml

@@ -1358,6 +1358,15 @@
   <value>${dfs.web.authentication.kerberos.principal}</value>
 </property>
 
+<property>
+  <name>dfs.namenode.kerberos.principal.pattern</name>
+  <value>*</value>
+  <description>
+    A client-side RegEx that can be configured to control
+    allowed realms to authenticate with (useful in cross-realm env.)
+  </description>
+</property>
+
 <property>
   <name>dfs.namenode.avoid.read.stale.datanode</name>
   <value>false</value>