From 5cc0c38417293a5ec893b1c7f62297b83aab9f4c Mon Sep 17 00:00:00 2001
From: Yang Wang <yang.wang@elastic.co>
Date: Thu, 28 Oct 2021 17:11:07 +1100
Subject: [PATCH] Skip automatically preserved request headers when rewriting
 (#79973)

In #79412 we fixed a bug that request headers got dropped when the
request is sent across to a node of different version. The fix is to
restore all existing request headers during the threadContext rewriting.
However, there are headers that are always automatically preserved by
the ThreadContext infrastructure, e.g. x-opaque-id. This causes failures
when the code tries to re-add the x-opaque-id header since it already
exists. An example of this issue is for CCS where the remote cluster is
often on a different version compared to the local cluster.

Resolves: #79412
---
 .../elasticsearch/xpack/core/security/SecurityContext.java | 3 +--
 .../elasticsearch/xpack/security/SecurityContextTests.java | 7 ++++++-
 2 files changed, 7 insertions(+), 3 deletions(-)

diff --git a/x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/security/SecurityContext.java b/x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/security/SecurityContext.java
index 59c62f61fe7c..e78cb5392f61 100644
--- a/x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/security/SecurityContext.java
+++ b/x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/security/SecurityContext.java
@@ -21,7 +21,6 @@
 import org.elasticsearch.xcontent.XContentType;
 import org.elasticsearch.xpack.core.security.authc.Authentication;
 import org.elasticsearch.xpack.core.security.authc.Authentication.AuthenticationType;
-import org.elasticsearch.xpack.core.security.authc.AuthenticationField;
 import org.elasticsearch.xpack.core.security.authc.support.AuthenticationContextSerializer;
 import org.elasticsearch.xpack.core.security.authc.support.SecondaryAuthentication;
 import org.elasticsearch.xpack.core.security.user.User;
@@ -175,7 +174,7 @@ public void executeAfterRewritingAuthentication(Consumer<StoredContext> consumer
                 )
             );
             existingRequestHeaders.forEach((k, v) -> {
-                if (false == AuthenticationField.AUTHENTICATION_KEY.equals(k)) {
+                if (threadContext.getHeader(k) == null) {
                     threadContext.putHeader(k, v);
                 }
             });
diff --git a/x-pack/plugin/security/src/test/java/org/elasticsearch/xpack/security/SecurityContextTests.java b/x-pack/plugin/security/src/test/java/org/elasticsearch/xpack/security/SecurityContextTests.java
index f64ad4572e78..f5e9255baf95 100644
--- a/x-pack/plugin/security/src/test/java/org/elasticsearch/xpack/security/SecurityContextTests.java
+++ b/x-pack/plugin/security/src/test/java/org/elasticsearch/xpack/security/SecurityContextTests.java
@@ -12,6 +12,7 @@
 import org.elasticsearch.common.settings.Settings;
 import org.elasticsearch.common.util.concurrent.ThreadContext;
 import org.elasticsearch.common.util.concurrent.ThreadContext.StoredContext;
+import org.elasticsearch.tasks.Task;
 import org.elasticsearch.test.ESTestCase;
 import org.elasticsearch.test.VersionUtils;
 import org.elasticsearch.xpack.core.security.SecurityContext;
@@ -124,7 +125,11 @@ public void testExecuteAfterRewritingAuthentication() throws IOException {
             AuthenticationField.PRIVILEGE_CATEGORY_KEY,
             randomAlphaOfLengthBetween(3, 10),
             randomAlphaOfLengthBetween(3, 8),
-            randomAlphaOfLengthBetween(3, 8)
+            randomAlphaOfLengthBetween(3, 8),
+            Task.X_OPAQUE_ID,
+            randomAlphaOfLength(10),
+            Task.TRACE_ID,
+            randomAlphaOfLength(20)
         );
         threadContext.putHeader(requestHeaders);