HADOOP-11291. Log the cause of SASL connection failures. Contributed by Stephen Chu.

hadoop-common-project/hadoop-common/CHANGES.txt

@@ -380,6 +380,9 @@ Release 2.7.0 - UNRELEASED
 
     HADOOP-10786. Fix UGI#reloginFromKeytab on Java 8. (Stephen Chu via wheat9)
 
+    HADOOP-11291. Log the cause of SASL connection failures.
+    (Stephen Chu via cnauroth)
+
   OPTIMIZATIONS
 
   BUG FIXES

hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/ipc/Client.java

@@ -668,7 +668,7 @@ public class Client {
               String msg = "Couldn't setup connection for "
                   + UserGroupInformation.getLoginUser().getUserName() + " to "
                   + remoteId;
-              LOG.warn(msg);
+              LOG.warn(msg, ex);
               throw (IOException) new IOException(msg).initCause(ex);
             }
           } else {