Minor wording suggestions

Author: Andrew Or

network/shuffle/src/main/java/org/apache/spark/network/sasl/ShuffleSecretManager.java

@@ -37,7 +37,7 @@ public class ShuffleSecretManager implements SecretKeyHolder {
   private static final Charset UTF8_CHARSET = Charset.forName("UTF-8");
 
   // Spark user used for authenticating SASL connections
-  // Note that this should match the value in org.apache.spark.SecurityManager
+  // Note that this must match the value in org.apache.spark.SecurityManager
   private static final String SPARK_SASL_USER = "sparkSaslUser";
 
   /**

yarn/alpha/src/main/scala/org/apache/spark/deploy/yarn/ExecutorRunnable.scala

@@ -91,8 +91,9 @@ class ExecutorRunnable(
 
     ctx.setApplicationACLs(YarnSparkHadoopUtil.getApplicationAclsForYarn(securityMgr))
 
-    // If external shuffle service is enabled, register with the
-    // Yarn shuffle service already started on the node manager
+    // If external shuffle service is enabled, register with the Yarn shuffle service already
+    // started on the NodeManager and, if authentication is enabled, provide it with our secret
+    // key for fetching shuffle files later
     if (sparkConf.getBoolean("spark.shuffle.service.enabled", false)) {
       val secretString = securityMgr.getSecretKey()
       val secretBytes =

yarn/stable/src/main/scala/org/apache/spark/deploy/yarn/ExecutorRunnable.scala

@@ -90,8 +90,9 @@ class ExecutorRunnable(
 
     ctx.setApplicationACLs(YarnSparkHadoopUtil.getApplicationAclsForYarn(securityMgr))
 
-    // If external shuffle service is enabled, register with the
-    // Yarn shuffle service already started on the node manager
+    // If external shuffle service is enabled, register with the Yarn shuffle service already
+    // started on the NodeManager and, if authentication is enabled, provide it with our secret
+    // key for fetching shuffle files later
     if (sparkConf.getBoolean("spark.shuffle.service.enabled", false)) {
       val secretString = securityMgr.getSecretKey()
       val secretBytes =