HDFS-14302. Refactor NameNodeWebHdfsMethods#generateDelegationToken() to allow better extensibility. Contributed by CR Hota.

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/web/resources/NamenodeWebHdfsMethods.java

@@ -350,12 +350,18 @@ public class NamenodeWebHdfsMethods {
     cp.cancelDelegationToken(token);
   }
 
-  public Token<? extends TokenIdentifier> generateDelegationToken(
-      final UserGroupInformation ugi,
+  public Credentials createCredentials(final UserGroupInformation ugi,
       final String renewer) throws IOException {
     final NameNode namenode = (NameNode)context.getAttribute("name.node");
     final Credentials c = DelegationTokenSecretManager.createCredentials(
         namenode, ugi, renewer != null? renewer: ugi.getShortUserName());
+    return c;
+  }
+
+  public Token<? extends TokenIdentifier> generateDelegationToken(
+      final UserGroupInformation ugi,
+      final String renewer) throws IOException {
+    Credentials c = createCredentials(ugi, renewer);
     if (c == null) {
       return null;
     }