unwrap CompletionException

Author: pan3793

hadoop-common-project/hadoop-auth/src/main/java/org/apache/hadoop/util/SubjectUtil.java

@@ -149,7 +149,17 @@ public static <T> T callAs(Subject subject, Callable<T> action) throws Completio
    * @return the result of the action
    */
   public static <T> T doAs(Subject subject, PrivilegedAction<T> action) {
-    return callAs(subject, privilegedActionToCallable(action));
+    try {
+      return callAs(subject, privilegedActionToCallable(action));
+    } catch (CompletionException ce) {
+      Exception cause = (Exception) (ce.getCause());
+      if (cause != null) {
+        throw sneakyThrow(cause);
+      } else {
+        // This should never happen, as CompletionException should always wrap an exception
+        throw ce;
+      }
+    }
   }
 
   /**