Add YARN-specific credential providers in debug logging message

Author: HyukjinKwon

core/src/main/scala/org/apache/spark/deploy/security/HadoopDelegationTokenManager.scala

@@ -32,7 +32,7 @@ import org.apache.spark.internal.Logging
  *
  * Also, each HadoopDelegationTokenProvider is controlled by
  * spark.security.credentials.{service}.enabled, and will not be loaded if this config is set to
- * false.  For example, Hive's delegation token provider [[HiveDelegationTokenProvider]] can be
+ * false. For example, Hive's delegation token provider [[HiveDelegationTokenProvider]] can be
  * enabled/disabled by the configuration spark.security.credentials.hive.enabled.
  *
  * @param sparkConf Spark configuration
@@ -52,7 +52,7 @@ private[spark] class HadoopDelegationTokenManager(
 
   // Maintain all the registered delegation token providers
   private val delegationTokenProviders = getDelegationTokenProviders
-  logDebug(s"Using the following delegation token providers: " +
+  logDebug(s"Using the following builtin delegation token providers: " +
     s"${delegationTokenProviders.keys.mkString(", ")}.")
 
   /** Construct a [[HadoopDelegationTokenManager]] for the default Hadoop filesystem */

resource-managers/yarn/src/main/scala/org/apache/spark/deploy/yarn/security/YARNHadoopDelegationTokenManager.scala

@@ -44,6 +44,8 @@ private[yarn] class YARNHadoopDelegationTokenManager(
 
   // public for testing
   val credentialProviders = getCredentialProviders
+  logDebug(s"Using the following YARN-specific credential providers: " +
+    s"${credentialProviders.keys.mkString(", ")}.")
 
   /**
    * Writes delegation tokens to creds.  Delegation tokens are fetched from all registered