diff --git a/Source/WebCore/ChangeLog b/Source/WebCore/ChangeLog
index 0bd242b..52b8265 100644
--- a/Source/WebCore/ChangeLog
+++ b/Source/WebCore/ChangeLog
@@ -1,3 +1,34 @@
+2019-05-16  Alex Christensen  <achristensen@webkit.org>
+
+        Add SPI to set a list of hosts to which to send custom header fields cross-origin
+        https://bugs.webkit.org/show_bug.cgi?id=197397
+
+        Reviewed by Geoff Garen.
+
+        In r223001 I added the ability to send custom headers, but with a restriction that they will not be sent except to the origin of the main document.
+        We need the ability to specify what origins to send these headers to even if they are not first party requests.
+        We get this information in a list of strings which are the hosts to send the headers to.  Some of the strings have an asterisk at the beginning,
+        indicating that the headers are to be sent to all subdomains.
+
+        I repurposed some ObjC SPI that was never adopted, but I keep testing the C API that was to verify no regression.
+        I also added some new API tests for the new behavior.
+
+        * Sources.txt:
+        * WebCore.xcodeproj/project.pbxproj:
+        * loader/CustomHeaderFields.cpp: Added.
+        (WebCore::CustomHeaderFields::thirdPartyDomainsMatch const):
+        * loader/CustomHeaderFields.h: Added.
+        (WebCore::CustomHeaderFields::encode const):
+        (WebCore::CustomHeaderFields::decode):
+        * loader/DocumentLoader.cpp:
+        (WebCore::DocumentLoader::setCustomHeaderFields): Deleted.
+        * loader/DocumentLoader.h:
+        (WebCore::DocumentLoader::setCustomHeaderFields):
+        (WebCore::DocumentLoader::customHeaderFields const):
+        (WebCore::DocumentLoader::customHeaderFields): Deleted.
+        * loader/cache/CachedResourceLoader.cpp:
+        (WebCore::CachedResourceLoader::requestResource):
+
 2019-05-16  Ali Juma  <ajuma@chromium.org>
 
         [IntersectionObserver] Regression: No initial observation when nothing else triggers rendering
diff --git a/Source/WebCore/Headers.cmake b/Source/WebCore/Headers.cmake
index 83dbea6..83427f0 100644
--- a/Source/WebCore/Headers.cmake
+++ b/Source/WebCore/Headers.cmake
@@ -654,6 +654,7 @@
     loader/CookieJar.h
     loader/CrossOriginAccessControl.h
     loader/CrossOriginPreflightResultCache.h
+    loader/CustomHeaderFields.h
     loader/DocumentLoader.h
     loader/DocumentWriter.h
     loader/EmptyClients.h
diff --git a/Source/WebCore/Sources.txt b/Source/WebCore/Sources.txt
index 7c3f89c..3675e00 100644
--- a/Source/WebCore/Sources.txt
+++ b/Source/WebCore/Sources.txt
@@ -1364,6 +1364,7 @@
 loader/CrossOriginAccessControl.cpp
 loader/CrossOriginPreflightChecker.cpp
 loader/CrossOriginPreflightResultCache.cpp
+loader/CustomHeaderFields.cpp @no-unify
 loader/DocumentLoader.cpp
 loader/DocumentThreadableLoader.cpp
 loader/DocumentWriter.cpp
diff --git a/Source/WebCore/WebCore.xcodeproj/project.pbxproj b/Source/WebCore/WebCore.xcodeproj/project.pbxproj
index 1403a66..f69cff2 100644
--- a/Source/WebCore/WebCore.xcodeproj/project.pbxproj
+++ b/Source/WebCore/WebCore.xcodeproj/project.pbxproj
@@ -1872,12 +1872,14 @@
 		5C4304B0191AC908000E2BC0 /* EXTShaderTextureLOD.cpp in Sources */ = {isa = PBXBuildFile; fileRef = 5C4304AD191AC908000E2BC0 /* EXTShaderTextureLOD.cpp */; };
 		5C4304B1191AC908000E2BC0 /* EXTShaderTextureLOD.h in Headers */ = {isa = PBXBuildFile; fileRef = 5C4304AE191AC908000E2BC0 /* EXTShaderTextureLOD.h */; };
 		5C4304B6191AEF46000E2BC0 /* JSEXTShaderTextureLOD.h in Headers */ = {isa = PBXBuildFile; fileRef = 5C4304B4191AEF46000E2BC0 /* JSEXTShaderTextureLOD.h */; };
+		5C5D2385227A0652000B9BDA /* CustomHeaderFields.h in Headers */ = {isa = PBXBuildFile; fileRef = 5C5D2383227A063A000B9BDA /* CustomHeaderFields.h */; settings = {ATTRIBUTES = (Private, ); }; };
 		5C7C88D81D0F1F4A009D2F6D /* SocketProvider.h in Headers */ = {isa = PBXBuildFile; fileRef = 5C7C88D71D0F1F2B009D2F6D /* SocketProvider.h */; settings = {ATTRIBUTES = (Private, ); }; };
 		5C9C2DB52241A67B00996B0B /* ContentRuleListResults.h in Headers */ = {isa = PBXBuildFile; fileRef = 5C9C2DB32241A67300996B0B /* ContentRuleListResults.h */; settings = {ATTRIBUTES = (Private, ); }; };
 		5C9EF2F321F06190003BDC56 /* StorageSessionProvider.h in Headers */ = {isa = PBXBuildFile; fileRef = 5C9EF2F221F06171003BDC56 /* StorageSessionProvider.h */; settings = {ATTRIBUTES = (Private, ); }; };
 		5CA1DEC61F71F1C700E71BD3 /* HTTPHeaderField.h in Headers */ = {isa = PBXBuildFile; fileRef = 5CA1DEC41F71E68700E71BD3 /* HTTPHeaderField.h */; settings = {ATTRIBUTES = (Private, ); }; };
 		5CB37FFF1C62D2A100F20188 /* ScrollAnimatorMock.h in Headers */ = {isa = PBXBuildFile; fileRef = 5CB37FFD1C62D27800F20188 /* ScrollAnimatorMock.h */; };
 		5CBC8DAD1AAA302200E1C803 /* MediaAccessibilitySoftLink.h in Headers */ = {isa = PBXBuildFile; fileRef = 5CBC8DAB1AAA302200E1C803 /* MediaAccessibilitySoftLink.h */; };
+		5CBD59592280E926002B22AA /* CustomHeaderFields.cpp in Sources */ = {isa = PBXBuildFile; fileRef = 5C5D2386227A077C000B9BDA /* CustomHeaderFields.cpp */; };
 		5CD9F5661AA0F73C00DA45FF /* DFABytecode.h in Headers */ = {isa = PBXBuildFile; fileRef = 5C39305D1AA0F6A90029C816 /* DFABytecode.h */; settings = {ATTRIBUTES = (Private, ); }; };
 		5CD9F5671AA0F74200DA45FF /* DFABytecodeCompiler.h in Headers */ = {isa = PBXBuildFile; fileRef = 5C39305F1AA0F6A90029C816 /* DFABytecodeCompiler.h */; settings = {ATTRIBUTES = (Private, ); }; };
 		5CD9F5681AA0F74600DA45FF /* DFABytecodeInterpreter.h in Headers */ = {isa = PBXBuildFile; fileRef = 5C3930611AA0F6A90029C816 /* DFABytecodeInterpreter.h */; settings = {ATTRIBUTES = (Private, ); }; };
@@ -8832,6 +8834,8 @@
 		5C5381B11D87D45700E2EBE6 /* URLSearchParams.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; path = URLSearchParams.h; sourceTree = "<group>"; };
 		5C5381B31D87E08100E2EBE6 /* JSURLSearchParams.cpp */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.cpp; path = JSURLSearchParams.cpp; sourceTree = "<group>"; };
 		5C5381B41D87E08100E2EBE6 /* JSURLSearchParams.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; path = JSURLSearchParams.h; sourceTree = "<group>"; };
+		5C5D2383227A063A000B9BDA /* CustomHeaderFields.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; path = CustomHeaderFields.h; sourceTree = "<group>"; };
+		5C5D2386227A077C000B9BDA /* CustomHeaderFields.cpp */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.cpp; path = CustomHeaderFields.cpp; sourceTree = "<group>"; };
 		5C668E641E7C6C3500D32B3B /* SocketStreamHandleImpl.cpp */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.cpp; path = SocketStreamHandleImpl.cpp; sourceTree = "<group>"; };
 		5C688AA01D380509000B54FA /* ThreadableWebSocketChannel.cpp */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.cpp; path = ThreadableWebSocketChannel.cpp; sourceTree = "<group>"; };
 		5C688AA21D38126F000B54FA /* SocketProvider.cpp */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.cpp; path = SocketProvider.cpp; sourceTree = "<group>"; };
@@ -25011,6 +25015,8 @@
 				41ABE67A1D0580D5006D862D /* CrossOriginPreflightChecker.h */,
 				E1C415DD0F655D7C0092D2FB /* CrossOriginPreflightResultCache.cpp */,
 				E1C415D90F655D6F0092D2FB /* CrossOriginPreflightResultCache.h */,
+				5C5D2386227A077C000B9BDA /* CustomHeaderFields.cpp */,
+				5C5D2383227A063A000B9BDA /* CustomHeaderFields.h */,
 				93E227DB0AF589AD00D48324 /* DocumentLoader.cpp */,
 				656D371E0ADBA5DE00A4554D /* DocumentLoader.h */,
 				0B9056150F2578BE0095FF6A /* DocumentThreadableLoader.cpp */,
@@ -28685,6 +28691,7 @@
 				93D437A01D57B19A00AB85EA /* CustomElementReactionQueue.h in Headers */,
 				9BD4E91B1C462CFC005065BC /* CustomElementRegistry.h in Headers */,
 				62CD325A1157E57C0063B0A7 /* CustomEvent.h in Headers */,
+				5C5D2385227A0652000B9BDA /* CustomHeaderFields.h in Headers */,
 				4B1E13E721790D660042CF98 /* CustomPaintCanvas.h in Headers */,
 				4B7AE4932177B56F00C59959 /* CustomPaintImage.h in Headers */,
 				A8CB413E0E8633FD0032C4F0 /* DashArray.h in Headers */,
@@ -32609,6 +32616,7 @@
 				07AFF4231EFB144900B545B3 /* CoreAudioCaptureSourceIOS.mm in Sources */,
 				46C696CC1E7205FC00597937 /* CPUMonitor.cpp in Sources */,
 				1ABA76CA11D20E50004C201C /* CSSPropertyNames.cpp in Sources */,
+				5CBD59592280E926002B22AA /* CustomHeaderFields.cpp in Sources */,
 				BE23480C18A9870B00E4B6E8 /* DataCue.cpp in Sources */,
 				4463CF682212FA68001A8577 /* DataDetectorsCoreSoftLink.mm in Sources */,
 				E58B45BB20AD07DD00991025 /* DataListButtonElement.cpp in Sources */,
diff --git a/Source/WebCore/loader/CustomHeaderFields.cpp b/Source/WebCore/loader/CustomHeaderFields.cpp
new file mode 100644
index 0000000..deee438
--- /dev/null
+++ b/Source/WebCore/loader/CustomHeaderFields.cpp
@@ -0,0 +1,52 @@
+/*
+ * Copyright (C) 2019 Apple Inc. All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY APPLE INC. AND ITS CONTRIBUTORS ``AS IS''
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
+ * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
+ * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR ITS CONTRIBUTORS
+ * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF
+ * THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include "config.h"
+#include "CustomHeaderFields.h"
+
+#include "HTTPHeaderField.h"
+#include "RegistrableDomain.h"
+
+namespace WebCore {
+
+bool CustomHeaderFields::thirdPartyDomainsMatch(const URL& url) const
+{
+    if (thirdPartyDomains.isEmpty())
+        return false;
+
+    auto registrableDomainLength = RegistrableDomain(url).string().length();
+    for (const auto& domainOrPattern : thirdPartyDomains) {
+        if (domainOrPattern == url.host())
+            return true;
+        if (domainOrPattern.startsWith("*.")
+            && url.host().endsWith(StringView(domainOrPattern).substring(1))
+            && domainOrPattern.length() > registrableDomainLength)
+            return true;
+    }
+
+    return false;
+}
+
+}
diff --git a/Source/WebCore/loader/CustomHeaderFields.h b/Source/WebCore/loader/CustomHeaderFields.h
new file mode 100644
index 0000000..660ff0a
--- /dev/null
+++ b/Source/WebCore/loader/CustomHeaderFields.h
@@ -0,0 +1,67 @@
+/*
+ * Copyright (C) 2019 Apple Inc. All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY APPLE INC. ``AS IS'' AND ANY
+ * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
+ * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL APPLE INC. OR
+ * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
+ * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
+ * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
+ * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
+ * OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#pragma once
+
+#include "HTTPHeaderField.h"
+#include <wtf/Vector.h>
+#include <wtf/text/WTFString.h>
+
+namespace WebCore {
+
+struct WEBCORE_EXPORT CustomHeaderFields {
+    Vector<HTTPHeaderField> fields;
+    Vector<String> thirdPartyDomains;
+
+    bool thirdPartyDomainsMatch(const URL&) const;
+
+    template<class Encoder> void encode(Encoder&) const;
+    template<class Decoder> static Optional<CustomHeaderFields> decode(Decoder&);
+};
+
+template<class Encoder>
+void CustomHeaderFields::encode(Encoder& encoder) const
+{
+    encoder << fields;
+    encoder << thirdPartyDomains;
+}
+
+template<class Decoder>
+Optional<CustomHeaderFields> CustomHeaderFields::decode(Decoder& decoder)
+{
+    Optional<Vector<HTTPHeaderField>> fields;
+    decoder >> fields;
+    if (!fields)
+        return WTF::nullopt;
+    
+    Optional<Vector<String>> thirdPartyDomains;
+    decoder >> thirdPartyDomains;
+    if (!thirdPartyDomains)
+        return WTF::nullopt;
+    
+    return {{ WTFMove(*fields), WTFMove(*thirdPartyDomains) }};
+}
+
+} // namespace WebCore
diff --git a/Source/WebCore/loader/DocumentLoader.cpp b/Source/WebCore/loader/DocumentLoader.cpp
index fceea1b..10cfdd9 100644
--- a/Source/WebCore/loader/DocumentLoader.cpp
+++ b/Source/WebCore/loader/DocumentLoader.cpp
@@ -38,6 +38,7 @@
 #include "CachedResourceLoader.h"
 #include "ContentExtensionError.h"
 #include "ContentSecurityPolicy.h"
+#include "CustomHeaderFields.h"
 #include "DOMWindow.h"
 #include "Document.h"
 #include "DocumentParser.h"
@@ -53,7 +54,6 @@
 #include "FrameTree.h"
 #include "HTMLFormElement.h"
 #include "HTMLFrameOwnerElement.h"
-#include "HTTPHeaderField.h"
 #include "HTTPHeaderNames.h"
 #include "HistoryItem.h"
 #include "HistoryController.h"
@@ -1322,11 +1322,6 @@
 }
 #endif
 
-void DocumentLoader::setCustomHeaderFields(Vector<HTTPHeaderField>&& fields)
-{
-    m_customHeaderFields = WTFMove(fields);
-}
-
 bool DocumentLoader::isLoadingInAPISense() const
 {
     // Once a frame has loaded, we no longer need to consider subresources,
diff --git a/Source/WebCore/loader/DocumentLoader.h b/Source/WebCore/loader/DocumentLoader.h
index b1445e7..8144382 100644
--- a/Source/WebCore/loader/DocumentLoader.h
+++ b/Source/WebCore/loader/DocumentLoader.h
@@ -76,10 +76,10 @@
 class CachedRawResource;
 class CachedResourceLoader;
 class ContentFilter;
+struct CustomHeaderFields;
 class FormState;
 class Frame;
 class FrameLoader;
-class HTTPHeaderField;
 class IconLoader;
 class Page;
 class PreviewConverter;
@@ -371,8 +371,8 @@
     void finishedLoadingApplicationManifest(ApplicationManifestLoader&);
 #endif
 
-    WEBCORE_EXPORT void setCustomHeaderFields(Vector<HTTPHeaderField>&& fields);
-    const Vector<HTTPHeaderField>& customHeaderFields() { return m_customHeaderFields; }
+    void setCustomHeaderFields(Vector<CustomHeaderFields>&& fields) { m_customHeaderFields = WTFMove(fields); }
+    const Vector<CustomHeaderFields>& customHeaderFields() const { return m_customHeaderFields; }
 
     void setAllowsWebArchiveForMainFrame(bool allowsWebArchiveForMainFrame) { m_allowsWebArchiveForMainFrame = allowsWebArchiveForMainFrame; }
     bool allowsWebArchiveForMainFrame() const { return m_allowsWebArchiveForMainFrame; }
@@ -564,7 +564,7 @@
     HashMap<std::unique_ptr<ApplicationManifestLoader>, uint64_t> m_applicationManifestLoaders;
 #endif
 
-    Vector<HTTPHeaderField> m_customHeaderFields;
+    Vector<CustomHeaderFields> m_customHeaderFields;
     
     bool m_subresourceLoadersArePageCacheAcceptable { false };
     ShouldOpenExternalURLsPolicy m_shouldOpenExternalURLsPolicy { ShouldOpenExternalURLsPolicy::ShouldNotAllow };
diff --git a/Source/WebCore/loader/cache/CachedResourceLoader.cpp b/Source/WebCore/loader/cache/CachedResourceLoader.cpp
index 5b0d4e0..843a9d1 100644
--- a/Source/WebCore/loader/cache/CachedResourceLoader.cpp
+++ b/Source/WebCore/loader/cache/CachedResourceLoader.cpp
@@ -43,6 +43,7 @@
 #include "ContentRuleListResults.h"
 #include "ContentSecurityPolicy.h"
 #include "CrossOriginAccessControl.h"
+#include "CustomHeaderFields.h"
 #include "DOMWindow.h"
 #include "DiagnosticLoggingClient.h"
 #include "DiagnosticLoggingKeys.h"
@@ -858,9 +859,11 @@
             sameOriginRequest = document()->topDocument().securityOrigin().isSameSchemeHostPort(requestedOrigin.get())
                 && document()->securityOrigin().isSameSchemeHostPort(requestedOrigin.get());
         }
-        if (sameOriginRequest) {
-            for (auto& field : m_documentLoader->customHeaderFields())
-                request.resourceRequest().setHTTPHeaderField(field.name(), field.value());
+        for (auto& fields : m_documentLoader->customHeaderFields()) {
+            if (sameOriginRequest || fields.thirdPartyDomainsMatch(url)) {
+                for (auto& field : fields.fields)
+                    request.resourceRequest().setHTTPHeaderField(field.name(), field.value());
+            }
         }
     }
 
diff --git a/Source/WebKit/ChangeLog b/Source/WebKit/ChangeLog
index cecd952..59b4370 100644
--- a/Source/WebKit/ChangeLog
+++ b/Source/WebKit/ChangeLog
@@ -1,3 +1,50 @@
+2019-05-16  Alex Christensen  <achristensen@webkit.org>
+
+        Add SPI to set a list of hosts to which to send custom header fields cross-origin
+        https://bugs.webkit.org/show_bug.cgi?id=197397
+
+        Reviewed by Geoff Garen.
+
+        * Shared/API/APIObject.h:
+        * Shared/Cocoa/APIObject.mm:
+        (API::Object::newObject):
+        * Shared/WebsitePoliciesData.cpp:
+        (WebKit::WebsitePoliciesData::decode):
+        * Shared/WebsitePoliciesData.h:
+        * SourcesCocoa.txt:
+        * UIProcess/API/APICustomHeaderFields.h: Added.
+        * UIProcess/API/APIWebsitePolicies.cpp:
+        (API::WebsitePolicies::WebsitePolicies):
+        (API::WebsitePolicies::copy const):
+        (API::WebsitePolicies::data):
+        * UIProcess/API/APIWebsitePolicies.h:
+        * UIProcess/API/C/WKWebsitePolicies.cpp:
+        (WKWebsitePoliciesCopyCustomHeaderFields):
+        (WKWebsitePoliciesSetCustomHeaderFields):
+        * UIProcess/API/Cocoa/WKWebpagePreferences.mm:
+        (-[WKWebpagePreferences _customHeaderFields]):
+        (-[WKWebpagePreferences _setCustomHeaderFields:]):
+        * UIProcess/API/Cocoa/WKWebpagePreferencesPrivate.h:
+        * UIProcess/API/Cocoa/_WKCustomHeaderFields.h: Added.
+        * UIProcess/API/Cocoa/_WKCustomHeaderFields.mm: Added.
+        (-[_WKCustomHeaderFields init]):
+        (-[_WKCustomHeaderFields dealloc]):
+        (-[_WKCustomHeaderFields fields]):
+        (-[_WKCustomHeaderFields setFields:]):
+        (-[_WKCustomHeaderFields thirdPartyDomains]):
+        (-[_WKCustomHeaderFields setThirdPartyDomains:]):
+        (-[_WKCustomHeaderFields _apiObject]):
+        * UIProcess/API/Cocoa/_WKCustomHeaderFieldsInternal.h: Added.
+        * UIProcess/API/Cocoa/_WKWebsitePolicies.h:
+        * UIProcess/API/Cocoa/_WKWebsitePolicies.mm:
+        (-[_WKWebsitePolicies customHeaderFields]): Deleted.
+        (-[_WKWebsitePolicies setCustomHeaderFields:]): Deleted.
+        * UIProcess/Cocoa/WebViewImpl.h:
+        * UIProcess/Cocoa/WebViewImpl.mm:
+        (WebKit::WebViewImpl::takeFocus):
+        (WebKit::WebViewImpl::accessibilityAttributeValue):
+        * WebKit.xcodeproj/project.pbxproj:
+
 2019-05-16  Ryan Walklin  <ryan@testtoast.com>
 
         [WPE] Rendering on a HiDPI display looks scaled up instead of rendered at 2x
diff --git a/Source/WebKit/Shared/API/APIObject.h b/Source/WebKit/Shared/API/APIObject.h
index 2ae85fc..de208c4 100644
--- a/Source/WebKit/Shared/API/APIObject.h
+++ b/Source/WebKit/Shared/API/APIObject.h
@@ -111,6 +111,7 @@
         ContentRuleListStore,
         ContextMenuListener,
         CookieManager,
+        CustomHeaderFields,
         InternalDebugFeature,
         Download,
         ExperimentalFeature,
diff --git a/Source/WebKit/Shared/Cocoa/APIObject.mm b/Source/WebKit/Shared/Cocoa/APIObject.mm
index 457fd0c..ee98ca3 100644
--- a/Source/WebKit/Shared/Cocoa/APIObject.mm
+++ b/Source/WebKit/Shared/Cocoa/APIObject.mm
@@ -70,6 +70,7 @@
 #import "_WKAttachmentInternal.h"
 #import "_WKAutomationSessionInternal.h"
 #import "_WKContentRuleListActionInternal.h"
+#import "_WKCustomHeaderFieldsInternal.h"
 #import "_WKDownloadInternal.h"
 #import "_WKExperimentalFeatureInternal.h"
 #import "_WKFrameHandleInternal.h"
@@ -312,6 +313,10 @@
         wrapper = [WKContentRuleListStore alloc];
         break;
 
+    case Type::CustomHeaderFields:
+        wrapper = [_WKCustomHeaderFields alloc];
+        break;
+
     case Type::UserContentWorld:
         wrapper = [_WKUserContentWorld alloc];
         break;
diff --git a/Source/WebKit/Shared/WebsitePoliciesData.cpp b/Source/WebKit/Shared/WebsitePoliciesData.cpp
index 5a54860..f53776a 100644
--- a/Source/WebKit/Shared/WebsitePoliciesData.cpp
+++ b/Source/WebKit/Shared/WebsitePoliciesData.cpp
@@ -28,6 +28,7 @@
 
 #include "ArgumentCoders.h"
 #include "WebProcess.h"
+#include <WebCore/CustomHeaderFields.h>
 #include <WebCore/DocumentLoader.h>
 #include <WebCore/Frame.h>
 #include <WebCore/Page.h>
@@ -77,7 +78,7 @@
     if (!allowedAutoplayQuirks)
         return WTF::nullopt;
     
-    Optional<Vector<WebCore::HTTPHeaderField>> customHeaderFields;
+    Optional<Vector<WebCore::CustomHeaderFields>> customHeaderFields;
     decoder >> customHeaderFields;
     if (!customHeaderFields)
         return WTF::nullopt;
diff --git a/Source/WebKit/Shared/WebsitePoliciesData.h b/Source/WebKit/Shared/WebsitePoliciesData.h
index 6a02fca..040bf06 100644
--- a/Source/WebKit/Shared/WebsitePoliciesData.h
+++ b/Source/WebKit/Shared/WebsitePoliciesData.h
@@ -32,8 +32,8 @@
 #include "WebsiteMetaViewportPolicy.h"
 #include "WebsitePopUpPolicy.h"
 #include "WebsiteSimulatedMouseEventsDispatchPolicy.h"
+#include <WebCore/CustomHeaderFields.h>
 #include <WebCore/DeviceOrientationOrMotionPermissionState.h>
-#include <WebCore/HTTPHeaderField.h>
 #include <wtf/OptionSet.h>
 
 namespace IPC {
@@ -56,7 +56,7 @@
 #if ENABLE(DEVICE_ORIENTATION)
     WebCore::DeviceOrientationOrMotionPermissionState deviceOrientationAndMotionAccessState;
 #endif
-    Vector<WebCore::HTTPHeaderField> customHeaderFields;
+    Vector<WebCore::CustomHeaderFields> customHeaderFields;
     WebsitePopUpPolicy popUpPolicy { WebsitePopUpPolicy::Default };
     Optional<WebsiteDataStoreParameters> websiteDataStoreParameters;
     String customUserAgent;
diff --git a/Source/WebKit/SourcesCocoa.txt b/Source/WebKit/SourcesCocoa.txt
index b81088e..d4a7723 100644
--- a/Source/WebKit/SourcesCocoa.txt
+++ b/Source/WebKit/SourcesCocoa.txt
@@ -242,6 +242,7 @@
 UIProcess/API/Cocoa/_WKAutomationSessionConfiguration.mm
 UIProcess/API/Cocoa/_WKContentRuleListAction.mm
 UIProcess/API/Cocoa/_WKContextMenuElementInfo.mm
+UIProcess/API/Cocoa/_WKCustomHeaderFields.mm @no-unify
 UIProcess/API/Cocoa/_WKDownload.mm
 UIProcess/API/Cocoa/_WKElementAction.mm
 UIProcess/API/Cocoa/_WKErrorRecoveryAttempting.mm
diff --git a/Source/WebKit/UIProcess/API/APICustomHeaderFields.h b/Source/WebKit/UIProcess/API/APICustomHeaderFields.h
new file mode 100644
index 0000000..1c4c2cd
--- /dev/null
+++ b/Source/WebKit/UIProcess/API/APICustomHeaderFields.h
@@ -0,0 +1,57 @@
+/*
+ * Copyright (C) 2019 Apple Inc. All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY APPLE INC. AND ITS CONTRIBUTORS ``AS IS''
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
+ * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
+ * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR ITS CONTRIBUTORS
+ * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF
+ * THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#pragma once
+
+#include "APIObject.h"
+#include <WebCore/CustomHeaderFields.h>
+
+namespace API {
+
+class CustomHeaderFields final : public ObjectImpl<Object::Type::CustomHeaderFields> {
+public:
+    template<typename... Args> static Ref<CustomHeaderFields> create(Args&&... args)
+    {
+        return adoptRef(*new CustomHeaderFields(std::forward<Args>(args)...));
+    }
+
+    CustomHeaderFields() = default;
+
+    const Vector<WebCore::HTTPHeaderField>& fields() const { return m_fields.fields; }
+    void setFields(Vector<WebCore::HTTPHeaderField>&& fields) { m_fields.fields = WTFMove(fields); }
+
+    const Vector<WTF::String> thirdPartyDomains() const { return m_fields.thirdPartyDomains; }
+    void setThirdPartyDomains(Vector<WTF::String>&& domains) { m_fields.thirdPartyDomains = WTFMove(domains); }
+
+    const WebCore::CustomHeaderFields& coreFields() const { return m_fields; }
+
+private:
+    CustomHeaderFields(const WebCore::CustomHeaderFields& fields)
+        : m_fields(fields) { }
+
+    WebCore::CustomHeaderFields m_fields;
+};
+
+} // namespace API
diff --git a/Source/WebKit/UIProcess/API/APIWebsitePolicies.cpp b/Source/WebKit/UIProcess/API/APIWebsitePolicies.cpp
index 99e830c..5cfeb08 100644
--- a/Source/WebKit/UIProcess/API/APIWebsitePolicies.cpp
+++ b/Source/WebKit/UIProcess/API/APIWebsitePolicies.cpp
@@ -33,10 +33,11 @@
 
 WebsitePolicies::WebsitePolicies() = default;
 
-WebsitePolicies::WebsitePolicies(bool contentBlockersEnabled, OptionSet<WebKit::WebsiteAutoplayQuirk> allowedAutoplayQuirks, WebKit::WebsiteAutoplayPolicy autoplayPolicy, Vector<WebCore::HTTPHeaderField>&& customHeaderFields, WebKit::WebsitePopUpPolicy popUpPolicy, RefPtr<WebsiteDataStore>&& websiteDataStore)
+WebsitePolicies::WebsitePolicies(bool contentBlockersEnabled, OptionSet<WebKit::WebsiteAutoplayQuirk> allowedAutoplayQuirks, WebKit::WebsiteAutoplayPolicy autoplayPolicy, Vector<WebCore::HTTPHeaderField>&& legacyCustomHeaderFields, Vector<WebCore::CustomHeaderFields>&& customHeaderFields, WebKit::WebsitePopUpPolicy popUpPolicy, RefPtr<WebsiteDataStore>&& websiteDataStore)
     : m_contentBlockersEnabled(contentBlockersEnabled)
     , m_allowedAutoplayQuirks(allowedAutoplayQuirks)
     , m_autoplayPolicy(autoplayPolicy)
+    , m_legacyCustomHeaderFields(WTFMove(legacyCustomHeaderFields))
     , m_customHeaderFields(WTFMove(customHeaderFields))
     , m_popUpPolicy(popUpPolicy)
     , m_websiteDataStore(WTFMove(websiteDataStore))
@@ -60,10 +61,17 @@
     policies->setMetaViewportPolicy(m_metaViewportPolicy);
     policies->setMediaSourcePolicy(m_mediaSourcePolicy);
     policies->setSimulatedMouseEventsDispatchPolicy(m_simulatedMouseEventsDispatchPolicy);
-    Vector<WebCore::HTTPHeaderField> customHeaderFields;
+    
+    Vector<WebCore::HTTPHeaderField> legacyCustomHeaderFields;
+    legacyCustomHeaderFields.reserveInitialCapacity(m_legacyCustomHeaderFields.size());
+    for (auto& field : m_legacyCustomHeaderFields)
+        legacyCustomHeaderFields.uncheckedAppend(field);
+    policies->setLegacyCustomHeaderFields(WTFMove(legacyCustomHeaderFields));
+
+    Vector<WebCore::CustomHeaderFields> customHeaderFields;
     customHeaderFields.reserveInitialCapacity(m_customHeaderFields.size());
     for (auto& field : m_customHeaderFields)
-        customHeaderFields.append(WebCore::HTTPHeaderField(field));
+        customHeaderFields.uncheckedAppend(field);
     policies->setCustomHeaderFields(WTFMove(customHeaderFields));
     policies->setAllowSiteSpecificQuirksToOverrideCompatibilityMode(m_allowSiteSpecificQuirksToOverrideCompatibilityMode);
     policies->setApplicationNameForUserAgentWithModernCompatibility(m_applicationNameForUserAgentWithModernCompatibility);
@@ -81,6 +89,14 @@
 
 WebKit::WebsitePoliciesData WebsitePolicies::data()
 {
+    bool hasLegacyCustomHeaderFields = legacyCustomHeaderFields().size();
+    Vector<WebCore::CustomHeaderFields> customHeaderFields;
+    customHeaderFields.reserveInitialCapacity(this->customHeaderFields().size() + hasLegacyCustomHeaderFields);
+    for (auto& field : this->customHeaderFields())
+        customHeaderFields.uncheckedAppend(field);
+    if (hasLegacyCustomHeaderFields)
+        customHeaderFields.uncheckedAppend({ legacyCustomHeaderFields(), { }});
+
     return {
         contentBlockersEnabled(),
         allowedAutoplayQuirks(),
@@ -88,7 +104,7 @@
 #if ENABLE(DEVICE_ORIENTATION)
         deviceOrientationAndMotionAccessState(),
 #endif
-        customHeaderFields(),
+        WTFMove(customHeaderFields),
         popUpPolicy(),
         m_websiteDataStore ? Optional<WebKit::WebsiteDataStoreParameters> { m_websiteDataStore->websiteDataStore().parameters() } : WTF::nullopt,
         m_customUserAgent,
diff --git a/Source/WebKit/UIProcess/API/APIWebsitePolicies.h b/Source/WebKit/UIProcess/API/APIWebsitePolicies.h
index 4d49269..50ff7ae 100644
--- a/Source/WebKit/UIProcess/API/APIWebsitePolicies.h
+++ b/Source/WebKit/UIProcess/API/APIWebsitePolicies.h
@@ -33,6 +33,7 @@
 #include "WebsiteMetaViewportPolicy.h"
 #include "WebsitePopUpPolicy.h"
 #include "WebsiteSimulatedMouseEventsDispatchPolicy.h"
+#include <WebCore/CustomHeaderFields.h>
 #include <WebCore/DeviceOrientationOrMotionPermissionState.h>
 #include <WebCore/HTTPHeaderField.h>
 #include <wtf/OptionSet.h>
@@ -68,9 +69,11 @@
     void setDeviceOrientationAndMotionAccessState(WebCore::DeviceOrientationOrMotionPermissionState state) { m_deviceOrientationAndMotionAccessState = state; }
 #endif
 
-    const Vector<WebCore::HTTPHeaderField>& customHeaderFields() const { return m_customHeaderFields; }
-    Vector<WebCore::HTTPHeaderField>&& takeCustomHeaderFields() { return WTFMove(m_customHeaderFields); }
-    void setCustomHeaderFields(Vector<WebCore::HTTPHeaderField>&& fields) { m_customHeaderFields = WTFMove(fields); }
+    const Vector<WebCore::HTTPHeaderField>& legacyCustomHeaderFields() const { return m_legacyCustomHeaderFields; }
+    void setLegacyCustomHeaderFields(Vector<WebCore::HTTPHeaderField>&& fields) { m_legacyCustomHeaderFields = WTFMove(fields); }
+
+    const Vector<WebCore::CustomHeaderFields>& customHeaderFields() const { return m_customHeaderFields; }
+    void setCustomHeaderFields(Vector<WebCore::CustomHeaderFields>&& fields) { m_customHeaderFields = WTFMove(fields); }
 
     WebKit::WebsitePopUpPolicy popUpPolicy() const { return m_popUpPolicy; }
     void setPopUpPolicy(WebKit::WebsitePopUpPolicy policy) { m_popUpPolicy = policy; }
@@ -108,7 +111,7 @@
     void setApplicationNameForUserAgentWithModernCompatibility(const WTF::String& applicationName) { m_applicationNameForUserAgentWithModernCompatibility = applicationName; }
 
 private:
-    WebsitePolicies(bool contentBlockersEnabled, OptionSet<WebKit::WebsiteAutoplayQuirk>, WebKit::WebsiteAutoplayPolicy, Vector<WebCore::HTTPHeaderField>&&, WebKit::WebsitePopUpPolicy, RefPtr<WebsiteDataStore>&&);
+    WebsitePolicies(bool contentBlockersEnabled, OptionSet<WebKit::WebsiteAutoplayQuirk>, WebKit::WebsiteAutoplayPolicy, Vector<WebCore::HTTPHeaderField>&&, Vector<WebCore::CustomHeaderFields>&&, WebKit::WebsitePopUpPolicy, RefPtr<WebsiteDataStore>&&);
 
     bool m_contentBlockersEnabled { true };
     OptionSet<WebKit::WebsiteAutoplayQuirk> m_allowedAutoplayQuirks;
@@ -116,7 +119,8 @@
 #if ENABLE(DEVICE_ORIENTATION)
     WebCore::DeviceOrientationOrMotionPermissionState m_deviceOrientationAndMotionAccessState { WebCore::DeviceOrientationOrMotionPermissionState::Prompt };
 #endif
-    Vector<WebCore::HTTPHeaderField> m_customHeaderFields;
+    Vector<WebCore::HTTPHeaderField> m_legacyCustomHeaderFields;
+    Vector<WebCore::CustomHeaderFields> m_customHeaderFields;
     WebKit::WebsitePopUpPolicy m_popUpPolicy { WebKit::WebsitePopUpPolicy::Default };
     RefPtr<WebsiteDataStore> m_websiteDataStore;
     WTF::String m_customUserAgent;
diff --git a/Source/WebKit/UIProcess/API/C/WKWebsitePolicies.cpp b/Source/WebKit/UIProcess/API/C/WKWebsitePolicies.cpp
index 64dbef8..aea4b8b 100644
--- a/Source/WebKit/UIProcess/API/C/WKWebsitePolicies.cpp
+++ b/Source/WebKit/UIProcess/API/C/WKWebsitePolicies.cpp
@@ -59,7 +59,7 @@
 WK_EXPORT WKDictionaryRef WKWebsitePoliciesCopyCustomHeaderFields(WKWebsitePoliciesRef websitePolicies)
 {
     HashMap<WTF::String, RefPtr<API::Object>> fields;
-    for (const auto& field : toImpl(websitePolicies)->customHeaderFields())
+    for (const auto& field : toImpl(websitePolicies)->legacyCustomHeaderFields())
         fields.add(field.name(), API::String::create(field.value()));
     return toAPI(API::Dictionary::create(WTFMove(fields)).ptr());
 }
@@ -76,7 +76,7 @@
         if (field && startsWithLettersIgnoringASCIICase(field->name(), "x-"))
             fields.uncheckedAppend(WTFMove(*field));
     }
-    toImpl(websitePolicies)->setCustomHeaderFields(WTFMove(fields));
+    toImpl(websitePolicies)->setLegacyCustomHeaderFields(WTFMove(fields));
 }
 
 void WKWebsitePoliciesSetAllowedAutoplayQuirks(WKWebsitePoliciesRef websitePolicies, WKWebsiteAutoplayQuirk allowedQuirks)
diff --git a/Source/WebKit/UIProcess/API/Cocoa/WKWebpagePreferences.mm b/Source/WebKit/UIProcess/API/Cocoa/WKWebpagePreferences.mm
index 6a36b1b..4c99139 100644
--- a/Source/WebKit/UIProcess/API/Cocoa/WKWebpagePreferences.mm
+++ b/Source/WebKit/UIProcess/API/Cocoa/WKWebpagePreferences.mm
@@ -26,9 +26,11 @@
 #import "config.h"
 #import "WKWebpagePreferences.h"
 
+#import "APICustomHeaderFields.h"
 #import "WKWebpagePreferencesInternal.h"
 #import "WKWebsiteDataStoreInternal.h"
 #import "WebCompatibilityMode.h"
+#import "_WKCustomHeaderFieldsInternal.h"
 #import "_WKWebsitePoliciesInternal.h"
 #import <wtf/RetainPtr.h>
 
@@ -214,26 +216,22 @@
     }
 }
 
-- (NSDictionary<NSString *, NSString *> *)_customHeaderFields
+- (NSArray<_WKCustomHeaderFields *> *)_customHeaderFields
 {
     const auto& fields = _websitePolicies->customHeaderFields();
-    auto dictionary = adoptNS([[NSMutableDictionary alloc] initWithCapacity:fields.size()]);
+    NSMutableArray *array = [[[NSMutableArray alloc] initWithCapacity:fields.size()] autorelease];
     for (const auto& field : fields)
-        [dictionary setObject:field.value() forKey:field.name()];
-    return dictionary.autorelease();
+        [array addObject:wrapper(API::CustomHeaderFields::create(field))];
+    return array;
 }
 
-- (void)_setCustomHeaderFields:(NSDictionary<NSString *, NSString *> *)fields
+- (void)_setCustomHeaderFields:(NSArray<_WKCustomHeaderFields *> *)fields
 {
-    Vector<WebCore::HTTPHeaderField> parsedFields;
-    parsedFields.reserveInitialCapacity(fields.count);
-
-    for (NSString *name in fields) {
-        auto field = WebCore::HTTPHeaderField::create(name, [fields objectForKey:name]);
-        if (field && startsWithLettersIgnoringASCIICase(field->name(), "x-"))
-            parsedFields.uncheckedAppend(WTFMove(*field));
-    }
-    _websitePolicies->setCustomHeaderFields(WTFMove(parsedFields));
+    Vector<WebCore::CustomHeaderFields> vector;
+    vector.reserveInitialCapacity(fields.count);
+    for (_WKCustomHeaderFields *element in fields)
+        vector.uncheckedAppend(static_cast<API::CustomHeaderFields&>([element _apiObject]).coreFields());
+    _websitePolicies->setCustomHeaderFields(WTFMove(vector));
 }
 
 - (WKWebsiteDataStore *)_websiteDataStore
diff --git a/Source/WebKit/UIProcess/API/Cocoa/WKWebpagePreferencesPrivate.h b/Source/WebKit/UIProcess/API/Cocoa/WKWebpagePreferencesPrivate.h
index 0bd0fac..2d5e249 100644
--- a/Source/WebKit/UIProcess/API/Cocoa/WKWebpagePreferencesPrivate.h
+++ b/Source/WebKit/UIProcess/API/Cocoa/WKWebpagePreferencesPrivate.h
@@ -55,12 +55,14 @@
     _WKWebsiteDeviceOrientationAndMotionAccessPolicyDeny,
 } WK_API_AVAILABLE(macos(10.14), ios(12.0));
 
+@class _WKCustomHeaderFields;
+
 @interface WKWebpagePreferences (WKPrivate)
 
 @property (nonatomic, setter=_setContentBlockersEnabled:) BOOL _contentBlockersEnabled;
 @property (nonatomic, setter=_setAllowedAutoplayQuirks:) _WKWebsiteAutoplayQuirk _allowedAutoplayQuirks;
 @property (nonatomic, setter=_setAutoplayPolicy:) _WKWebsiteAutoplayPolicy _autoplayPolicy;
-@property (nonatomic, copy, setter=_setCustomHeaderFields:) NSDictionary<NSString *, NSString *> *_customHeaderFields;
+@property (nonatomic, copy, setter=_setCustomHeaderFields:) NSArray<_WKCustomHeaderFields *> *_customHeaderFields;
 @property (nonatomic, setter=_setPopUpPolicy:) _WKWebsitePopUpPolicy _popUpPolicy;
 @property (nonatomic, strong, setter=_setWebsiteDataStore:) WKWebsiteDataStore *_websiteDataStore;
 @property (nonatomic, copy, setter=_setCustomUserAgent:) NSString *_customUserAgent;
diff --git a/Source/WebKit/UIProcess/API/Cocoa/_WKCustomHeaderFields.h b/Source/WebKit/UIProcess/API/Cocoa/_WKCustomHeaderFields.h
new file mode 100644
index 0000000..24355b0
--- /dev/null
+++ b/Source/WebKit/UIProcess/API/Cocoa/_WKCustomHeaderFields.h
@@ -0,0 +1,38 @@
+/*
+ * Copyright (C) 2019 Apple Inc. All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY APPLE INC. AND ITS CONTRIBUTORS ``AS IS''
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
+ * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
+ * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR ITS CONTRIBUTORS
+ * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF
+ * THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#import <WebKit/WKFoundation.h>
+
+NS_ASSUME_NONNULL_BEGIN
+
+WK_CLASS_AVAILABLE(macos(WK_MAC_TBA), ios(WK_IOS_TBA))
+@interface _WKCustomHeaderFields : NSObject
+
+@property (nonatomic, copy) NSDictionary<NSString *, NSString *> *fields;
+@property (nonatomic, copy) NSArray<NSString *> *thirdPartyDomains;
+
+@end
+
+NS_ASSUME_NONNULL_END
diff --git a/Source/WebKit/UIProcess/API/Cocoa/_WKCustomHeaderFields.mm b/Source/WebKit/UIProcess/API/Cocoa/_WKCustomHeaderFields.mm
new file mode 100644
index 0000000..ddef71f
--- /dev/null
+++ b/Source/WebKit/UIProcess/API/Cocoa/_WKCustomHeaderFields.mm
@@ -0,0 +1,92 @@
+/*
+ * Copyright (C) 2019 Apple Inc. All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY APPLE INC. AND ITS CONTRIBUTORS ``AS IS''
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
+ * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
+ * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR ITS CONTRIBUTORS
+ * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF
+ * THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#import "config.h"
+#import "_WKCustomHeaderFields.h"
+
+#import "_WKCustomHeaderFieldsInternal.h"
+#import <wtf/BlockPtr.h>
+
+@implementation _WKCustomHeaderFields
+
+- (instancetype)init
+{
+    if (!(self = [super init]))
+        return nil;
+    
+    API::Object::constructInWrapper<API::CustomHeaderFields>(self);
+    return self;
+}
+
+- (void)dealloc
+{
+    _fields->API::CustomHeaderFields::~CustomHeaderFields();
+    [super dealloc];
+}
+
+- (NSDictionary<NSString *, NSString *> *)fields
+{
+    auto& vector = _fields->fields();
+    NSMutableDictionary<NSString *, NSString *> *dictionary = [NSMutableDictionary dictionaryWithCapacity:vector.size()];
+    for (auto& field : vector)
+        [dictionary setObject:field.value() forKey:field.name()];
+    return dictionary;
+}
+
+- (void)setFields:(NSDictionary<NSString *, NSString *> *)fields
+{
+    Vector<WebCore::HTTPHeaderField> vector;
+    vector.reserveInitialCapacity(fields.count);
+    [fields enumerateKeysAndObjectsUsingBlock:makeBlockPtr([&](id key, id value, BOOL* stop) {
+        if (auto field = WebCore::HTTPHeaderField::create((NSString *)key, (NSString *)value); field && startsWithLettersIgnoringASCIICase(field->name(), "x-"))
+            vector.uncheckedAppend(WTFMove(*field));
+    }).get()];
+    _fields->setFields(WTFMove(vector));
+}
+
+- (NSArray<NSString *> *)thirdPartyDomains
+{
+    auto& domains = _fields->thirdPartyDomains();
+    NSMutableArray *array = [NSMutableArray arrayWithCapacity:domains.size()];
+    for (auto& domain : domains)
+        [array addObject:domain];
+    return array;
+}
+
+- (void)setThirdPartyDomains:(NSArray<NSString *> *)thirdPartyDomains
+{
+    Vector<String> domains;
+    domains.reserveInitialCapacity(thirdPartyDomains.count);
+    for (NSString *domain in thirdPartyDomains)
+        domains.uncheckedAppend(domain);
+    _fields->setThirdPartyDomains(WTFMove(domains));
+}
+
+- (API::Object&)_apiObject
+{
+    return *_fields;
+}
+
+@end
diff --git a/Source/WebKit/UIProcess/API/Cocoa/_WKCustomHeaderFieldsInternal.h b/Source/WebKit/UIProcess/API/Cocoa/_WKCustomHeaderFieldsInternal.h
new file mode 100644
index 0000000..05ef77a
--- /dev/null
+++ b/Source/WebKit/UIProcess/API/Cocoa/_WKCustomHeaderFieldsInternal.h
@@ -0,0 +1,42 @@
+/*
+ * Copyright (C) 2019 Apple Inc. All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY APPLE INC. AND ITS CONTRIBUTORS ``AS IS''
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
+ * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
+ * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR ITS CONTRIBUTORS
+ * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF
+ * THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#import "APICustomHeaderFields.h"
+#import "WKObject.h"
+#import "_WKCustomHeaderFields.h"
+
+namespace WebKit {
+
+template<> struct WrapperTraits<API::CustomHeaderFields> {
+    using WrapperClass = _WKCustomHeaderFields;
+};
+
+}
+
+@interface _WKCustomHeaderFields () <WKObject> {
+@package
+    API::ObjectStorage<API::CustomHeaderFields> _fields;
+}
+@end
diff --git a/Source/WebKit/UIProcess/API/Cocoa/_WKWebsitePolicies.mm b/Source/WebKit/UIProcess/API/Cocoa/_WKWebsitePolicies.mm
index c57bd9d..1435549 100644
--- a/Source/WebKit/UIProcess/API/Cocoa/_WKWebsitePolicies.mm
+++ b/Source/WebKit/UIProcess/API/Cocoa/_WKWebsitePolicies.mm
@@ -97,12 +97,24 @@
 
 - (NSDictionary<NSString *, NSString *> *)customHeaderFields
 {
-    return [_webpagePreferences _customHeaderFields];
+    auto& fields = static_cast<API::WebsitePolicies&>([_webpagePreferences _apiObject]).legacyCustomHeaderFields();
+    auto dictionary = [NSMutableDictionary dictionaryWithCapacity:fields.size()];
+    for (const auto& field : fields)
+        [dictionary setObject:field.value() forKey:field.name()];
+    return dictionary;
 }
 
 - (void)setCustomHeaderFields:(NSDictionary<NSString *, NSString *> *)fields
 {
-    [_webpagePreferences _setCustomHeaderFields:fields];
+    auto websitePolicies = static_cast<API::WebsitePolicies&>([_webpagePreferences _apiObject]);
+    Vector<WebCore::HTTPHeaderField> parsedFields;
+    parsedFields.reserveInitialCapacity(fields.count);
+    for (NSString *name in fields) {
+        auto field = WebCore::HTTPHeaderField::create(name, [fields objectForKey:name]);
+        if (field && startsWithLettersIgnoringASCIICase(field->name(), "x-"))
+            parsedFields.uncheckedAppend(WTFMove(*field));
+    }
+    websitePolicies.setLegacyCustomHeaderFields(WTFMove(parsedFields));
 }
 
 - (WKWebsiteDataStore *)websiteDataStore
diff --git a/Source/WebKit/WebKit.xcodeproj/project.pbxproj b/Source/WebKit/WebKit.xcodeproj/project.pbxproj
index 26c05c7..17ecd2e 100644
--- a/Source/WebKit/WebKit.xcodeproj/project.pbxproj
+++ b/Source/WebKit/WebKit.xcodeproj/project.pbxproj
@@ -1078,6 +1078,7 @@
 		5C5CEC33220912B300D6BBB0 /* AuxiliaryProcessMain.cpp in Sources */ = {isa = PBXBuildFile; fileRef = 5C5CEC31220912AF00D6BBB0 /* AuxiliaryProcessMain.cpp */; };
 		5C5CEC34220912B400D6BBB0 /* AuxiliaryProcessMain.cpp in Sources */ = {isa = PBXBuildFile; fileRef = 5C5CEC31220912AF00D6BBB0 /* AuxiliaryProcessMain.cpp */; };
 		5C5CEC35220912B400D6BBB0 /* AuxiliaryProcessMain.cpp in Sources */ = {isa = PBXBuildFile; fileRef = 5C5CEC31220912AF00D6BBB0 /* AuxiliaryProcessMain.cpp */; };
+		5C5D238C227A2CDA000B9BDA /* _WKCustomHeaderFields.h in Headers */ = {isa = PBXBuildFile; fileRef = 5C5D2389227A1892000B9BDA /* _WKCustomHeaderFields.h */; settings = {ATTRIBUTES = (Private, ); }; };
 		5C62FDF91EFC271C00CE072E /* WKURLSchemeTaskPrivate.h in Headers */ = {isa = PBXBuildFile; fileRef = 5C62FDF81EFC263C00CE072E /* WKURLSchemeTaskPrivate.h */; settings = {ATTRIBUTES = (Private, ); }; };
 		5C7FB47021E97DC5009E3241 /* WebCookieJar.h in Headers */ = {isa = PBXBuildFile; fileRef = 5C7FB46F21E97C0C009E3241 /* WebCookieJar.h */; };
 		5C8BC797218CBB4800813886 /* SafeBrowsing.xcassets in Resources */ = {isa = PBXBuildFile; fileRef = 5C8BC796218CB58A00813886 /* SafeBrowsing.xcassets */; };
@@ -1092,6 +1093,7 @@
 		5CB2378C1DF0DE6E00117AA3 /* _WKWebsitePolicies.h in Headers */ = {isa = PBXBuildFile; fileRef = 5CB237891DF0DD4300117AA3 /* _WKWebsitePolicies.h */; settings = {ATTRIBUTES = (Private, ); }; };
 		5CB2378E1DF0E0D300117AA3 /* _WKWebsitePoliciesInternal.h in Headers */ = {isa = PBXBuildFile; fileRef = 5CB2378D1DF0E0C200117AA3 /* _WKWebsitePoliciesInternal.h */; };
 		5CBC9B8E1C652CA000A8FDCF /* NetworkDataTask.h in Headers */ = {isa = PBXBuildFile; fileRef = 5CBC9B891C6524A500A8FDCF /* NetworkDataTask.h */; };
+		5CBD595C2280EDF4002B22AA /* _WKCustomHeaderFields.mm in Sources */ = {isa = PBXBuildFile; fileRef = 5C5D2388227A1892000B9BDA /* _WKCustomHeaderFields.mm */; };
 		5CD286511E7235990094FDC8 /* WKContentRuleListStore.h in Headers */ = {isa = PBXBuildFile; fileRef = 5CD2864D1E722F440094FDC8 /* WKContentRuleListStore.h */; settings = {ATTRIBUTES = (Public, ); }; };
 		5CD286531E7235AA0094FDC8 /* _WKUserContentFilterPrivate.h in Headers */ = {isa = PBXBuildFile; fileRef = 5CD286491E722F440094FDC8 /* _WKUserContentFilterPrivate.h */; settings = {ATTRIBUTES = (Private, ); }; };
 		5CD286541E7235B10094FDC8 /* WKContentRuleList.h in Headers */ = {isa = PBXBuildFile; fileRef = 5CD2864A1E722F440094FDC8 /* WKContentRuleList.h */; settings = {ATTRIBUTES = (Public, ); }; };
@@ -3528,6 +3530,10 @@
 		5C5CEC31220912AF00D6BBB0 /* AuxiliaryProcessMain.cpp */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.cpp; name = AuxiliaryProcessMain.cpp; path = Cocoa/AuxiliaryProcessMain.cpp; sourceTree = "<group>"; };
 		5C5CEC382209583200D6BBB0 /* DaemonEntryPoint.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; path = DaemonEntryPoint.h; sourceTree = "<group>"; };
 		5C5CEC392209583200D6BBB0 /* DaemonEntryPoint.mm */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.objcpp; path = DaemonEntryPoint.mm; sourceTree = "<group>"; };
+		5C5D2387227A1891000B9BDA /* _WKCustomHeaderFieldsInternal.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; path = _WKCustomHeaderFieldsInternal.h; sourceTree = "<group>"; };
+		5C5D2388227A1892000B9BDA /* _WKCustomHeaderFields.mm */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.objcpp; path = _WKCustomHeaderFields.mm; sourceTree = "<group>"; };
+		5C5D2389227A1892000B9BDA /* _WKCustomHeaderFields.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; path = _WKCustomHeaderFields.h; sourceTree = "<group>"; };
+		5C5D238A227A1D9B000B9BDA /* APICustomHeaderFields.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; path = APICustomHeaderFields.h; sourceTree = "<group>"; };
 		5C62FDF81EFC263C00CE072E /* WKURLSchemeTaskPrivate.h */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.c.h; path = WKURLSchemeTaskPrivate.h; sourceTree = "<group>"; };
 		5C6CE6D01F59BC460007C6CB /* PageClientImplCocoa.mm */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.objcpp; path = PageClientImplCocoa.mm; sourceTree = "<group>"; };
 		5C6CE6D31F59EA350007C6CB /* PageClientImplCocoa.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; path = PageClientImplCocoa.h; sourceTree = "<group>"; };
@@ -6141,6 +6147,9 @@
 				5C4609E422430E4D009943C2 /* _WKContentRuleListActionInternal.h */,
 				1A5704F61BE01FF400874AF1 /* _WKContextMenuElementInfo.h */,
 				1A5704F51BE01FF400874AF1 /* _WKContextMenuElementInfo.mm */,
+				5C5D2389227A1892000B9BDA /* _WKCustomHeaderFields.h */,
+				5C5D2388227A1892000B9BDA /* _WKCustomHeaderFields.mm */,
+				5C5D2387227A1891000B9BDA /* _WKCustomHeaderFieldsInternal.h */,
 				83891B681A68BEBC0030F386 /* _WKDiagnosticLoggingDelegate.h */,
 				A1A4FE5718DCE9FA00B5EA8A /* _WKDownload.h */,
 				A1A4FE5818DCE9FA00B5EA8A /* _WKDownload.mm */,
@@ -7705,6 +7714,7 @@
 				7C3A06A51AAB903E009D74BA /* APIContentRuleListStore.cpp */,
 				7C3A06A61AAB903E009D74BA /* APIContentRuleListStore.h */,
 				076E884D1A13CADF005E90FC /* APIContextMenuClient.h */,
+				5C5D238A227A1D9B000B9BDA /* APICustomHeaderFields.h */,
 				7A821F4F1E2F7A5C00604577 /* APICustomProtocolManagerClient.h */,
 				83891B621A68B3420030F386 /* APIDiagnosticLoggingClient.h */,
 				1F7D36C018DA513F00D9D659 /* APIDownloadClient.h */,
@@ -9018,6 +9028,7 @@
 				5C4609E7224317B4009943C2 /* _WKContentRuleListAction.h in Headers */,
 				5C4609E8224317BB009943C2 /* _WKContentRuleListActionInternal.h in Headers */,
 				1A5704F81BE01FF400874AF1 /* _WKContextMenuElementInfo.h in Headers */,
+				5C5D238C227A2CDA000B9BDA /* _WKCustomHeaderFields.h in Headers */,
 				83891B691A68BEBC0030F386 /* _WKDiagnosticLoggingDelegate.h in Headers */,
 				A1A4FE5A18DCE9FA00B5EA8A /* _WKDownload.h in Headers */,
 				A1A4FE6118DD54A400B5EA8A /* _WKDownloadDelegate.h in Headers */,
@@ -10957,6 +10968,7 @@
 			isa = PBXSourcesBuildPhase;
 			buildActionMask = 2147483647;
 			files = (
+				5CBD595C2280EDF4002B22AA /* _WKCustomHeaderFields.mm in Sources */,
 				99E7189A21F79D9E0055E975 /* _WKTouchEventGenerator.mm in Sources */,
 				2D92A784212B6AB100F493FD /* ActivityAssertion.cpp in Sources */,
 				2D92A77B212B6A7100F493FD /* ArgumentCoders.cpp in Sources */,
diff --git a/Tools/ChangeLog b/Tools/ChangeLog
index 912093f..80a3627 100644
--- a/Tools/ChangeLog
+++ b/Tools/ChangeLog
@@ -1,3 +1,18 @@
+2019-05-16  Alex Christensen  <achristensen@webkit.org>
+
+        Add SPI to set a list of hosts to which to send custom header fields cross-origin
+        https://bugs.webkit.org/show_bug.cgi?id=197397
+
+        Reviewed by Geoff Garen.
+
+        * TestWebKitAPI/Tests/WebKitCocoa/WebsitePolicies.mm:
+        (TEST):
+        (expectLegacyHeaders):
+        (expectHeaders):
+        (-[CustomHeaderFieldsDelegate webView:decidePolicyForNavigationAction:preferences:decisionHandler:]):
+        (-[CustomHeaderFieldsDelegate webView:startURLSchemeTask:]):
+        (-[CustomHeaderFieldsDelegate _webView:decidePolicyForNavigationAction:decisionHandler:]): Deleted.
+
 2019-05-15  Aakash Jain  <aakash_jain@apple.com>
 
         Replace double-quotes with single quotes in steps.py
diff --git a/Tools/TestWebKitAPI/Tests/WebKitCocoa/WebsitePolicies.mm b/Tools/TestWebKitAPI/Tests/WebKitCocoa/WebsitePolicies.mm
index 134319f..beb312a 100644
--- a/Tools/TestWebKitAPI/Tests/WebKitCocoa/WebsitePolicies.mm
+++ b/Tools/TestWebKitAPI/Tests/WebKitCocoa/WebsitePolicies.mm
@@ -28,16 +28,19 @@
 #import "PlatformUtilities.h"
 #import "TestNavigationDelegate.h"
 #import "TestWKWebView.h"
+#import <WebKit/WKMutableDictionary.h>
 #import <WebKit/WKNavigationDelegatePrivate.h>
 #import <WebKit/WKPagePrivate.h>
 #import <WebKit/WKPreferencesPrivate.h>
 #import <WebKit/WKPreferencesRefPrivate.h>
+#import <WebKit/WKString.h>
 #import <WebKit/WKUIDelegatePrivate.h>
 #import <WebKit/WKURLSchemeTaskPrivate.h>
 #import <WebKit/WKUserContentControllerPrivate.h>
 #import <WebKit/WKWebViewPrivate.h>
 #import <WebKit/WKWebsiteDataStorePrivate.h>
 #import <WebKit/WKWebsitePolicies.h>
+#import <WebKit/_WKCustomHeaderFields.h>
 #import <WebKit/_WKUserContentExtensionStorePrivate.h>
 #import <WebKit/_WKWebsiteDataStoreConfiguration.h>
 #import <WebKit/_WKWebsitePolicies.h>
@@ -907,9 +910,9 @@
 
 TEST(WebKit, InvalidCustomHeaders)
 {
-    auto websitePolicies = adoptNS([[_WKWebsitePolicies alloc] init]);
-    [websitePolicies setCustomHeaderFields:@{@"invalidheader" : @"", @"noncustom" : @"header", @"    x-Custom ":@"  Needs Canonicalization\t ", @"x-other" : @"other value"}];
-    NSDictionary<NSString *, NSString *> *canonicalized = [websitePolicies customHeaderFields];
+    auto customHeaderFields = adoptNS([[_WKCustomHeaderFields alloc] init]);
+    [customHeaderFields setFields:@{@"invalidheader" : @"", @"noncustom" : @"header", @"    x-Custom ":@"  Needs Canonicalization\t ", @"x-other" : @"other value"}];
+    NSDictionary<NSString *, NSString *> *canonicalized = [customHeaderFields fields];
     EXPECT_EQ(canonicalized.count, 2u);
     EXPECT_STREQ([canonicalized objectForKey:@"x-Custom"].UTF8String, "Needs Canonicalization");
     EXPECT_STREQ([canonicalized objectForKey:@"x-other"].UTF8String, "other value");
@@ -919,8 +922,9 @@
 static bool secondTestDone;
 static bool thirdTestDone;
 static bool fourthTestDone;
+static bool fifthTestDone;
 
-static void expectHeaders(id <WKURLSchemeTask> task, bool expected)
+static void expectLegacyHeaders(id <WKURLSchemeTask> task, bool expected)
 {
     NSURLRequest *request = task.request;
     if (expected) {
@@ -932,6 +936,18 @@
     }
 }
 
+static void expectHeaders(id <WKURLSchemeTask> task, bool expected)
+{
+    NSURLRequest *request = task.request;
+    if (expected) {
+        EXPECT_STREQ([[request valueForHTTPHeaderField:@"X-key3"] UTF8String], "value3");
+        EXPECT_STREQ([[request valueForHTTPHeaderField:@"X-key4"] UTF8String], "value4");
+    } else {
+        EXPECT_TRUE([request valueForHTTPHeaderField:@"X-key3"] == nil);
+        EXPECT_TRUE([request valueForHTTPHeaderField:@"X-key4"] == nil);
+    }
+}
+
 static void respond(id <WKURLSchemeTask>task, NSString *html = nil)
 {
     [task didReceiveResponse:[[[NSURLResponse alloc] initWithURL:task.request.URL MIMEType:@"text/html" expectedContentLength:html.length textEncodingName:nil] autorelease]];
@@ -944,61 +960,92 @@
 
 @implementation CustomHeaderFieldsDelegate
 
-IGNORE_WARNINGS_BEGIN("deprecated-implementations")
-- (void)_webView:(WKWebView *)webView decidePolicyForNavigationAction:(WKNavigationAction *)navigationAction decisionHandler:(void (^)(WKNavigationActionPolicy, _WKWebsitePolicies *))decisionHandler
-IGNORE_WARNINGS_END
+- (void)webView:(WKWebView *)webView decidePolicyForNavigationAction:(WKNavigationAction *)navigationAction preferences:(WKWebpagePreferences *)preferences decisionHandler:(void (^)(WKNavigationActionPolicy, WKWebpagePreferences *))decisionHandler
 {
-    _WKWebsitePolicies *websitePolicies = [[[_WKWebsitePolicies alloc] init] autorelease];
-    [websitePolicies setCustomHeaderFields:@{@"X-key1": @"value1", @"X-key2": @"value2"}];
+    auto legacyHeaderFieldDictionary = adoptWK(WKMutableDictionaryCreate());
+    WKDictionarySetItem(legacyHeaderFieldDictionary.get(), adoptWK(WKStringCreateWithUTF8CString("X-key1")).get(), adoptWK(WKStringCreateWithUTF8CString("value1")).get());
+    WKDictionarySetItem(legacyHeaderFieldDictionary.get(), adoptWK(WKStringCreateWithUTF8CString("X-key2")).get(), adoptWK(WKStringCreateWithUTF8CString("value2")).get());
+    WKWebsitePoliciesSetCustomHeaderFields((WKWebsitePoliciesRef)preferences, legacyHeaderFieldDictionary.get());
+
+    _WKCustomHeaderFields *headerFields = [[[_WKCustomHeaderFields alloc] init] autorelease];
+    [headerFields setFields:@{@"X-key3": @"value3", @"X-key4": @"value4"}];
+    [headerFields setThirdPartyDomains:@[
+        @"*.hostwithasterisk.com",
+        @"hostwithoutasterisk.com",
+        @"*.com" // should be ignored.
+    ]];
+    
+    [preferences _setCustomHeaderFields:@[headerFields]];
+    
     if ([navigationAction.request.URL.path isEqualToString:@"/mainresource"]) {
         dispatch_async(dispatch_get_main_queue(), ^{
-            decisionHandler(WKNavigationActionPolicyAllow, websitePolicies);
+            decisionHandler(WKNavigationActionPolicyAllow, preferences);
         });
     } else
-        decisionHandler(WKNavigationActionPolicyAllow, websitePolicies);
+        decisionHandler(WKNavigationActionPolicyAllow, preferences);
 }
 
 - (void)webView:(WKWebView *)webView startURLSchemeTask:(id <WKURLSchemeTask>)urlSchemeTask
 {
     NSString *path = urlSchemeTask.request.URL.path;
     if ([path isEqualToString:@"/mainresource"]) {
-        expectHeaders(urlSchemeTask, true);
+        expectLegacyHeaders(urlSchemeTask, true);
         respond(urlSchemeTask, @"<script>fetch('subresource').then(function(response){fetch('test://differentsecurityorigin/crossoriginsubresource',{mode:'no-cors'})})</script>");
     } else if ([path isEqualToString:@"/subresource"]) {
-        expectHeaders(urlSchemeTask, true);
+        expectLegacyHeaders(urlSchemeTask, true);
         respond(urlSchemeTask);
     } else if ([path isEqualToString:@"/crossoriginsubresource"]) {
-        expectHeaders(urlSchemeTask, false);
+        expectLegacyHeaders(urlSchemeTask, false);
         respond(urlSchemeTask);
         firstTestDone = true;
     } else if ([path isEqualToString:@"/mainresourcewithiframe"]) {
-        expectHeaders(urlSchemeTask, true);
+        expectLegacyHeaders(urlSchemeTask, true);
         respond(urlSchemeTask, @"<iframe src='test://iframeorigin/iframemainresource'></iframe>");
     } else if ([path isEqualToString:@"/iframemainresource"]) {
-        expectHeaders(urlSchemeTask, false);
+        expectLegacyHeaders(urlSchemeTask, false);
         respond(urlSchemeTask, @"<script>fetch('iframesubresource').then(function(response){fetch('test://mainframeorigin/originaloriginsubresource',{mode:'no-cors'})})</script>");
     } else if ([path isEqualToString:@"/iframesubresource"]) {
-        expectHeaders(urlSchemeTask, false);
+        expectLegacyHeaders(urlSchemeTask, false);
         respond(urlSchemeTask);
     } else if ([path isEqualToString:@"/originaloriginsubresource"]) {
-        expectHeaders(urlSchemeTask, false);
+        expectLegacyHeaders(urlSchemeTask, false);
         respond(urlSchemeTask);
         secondTestDone = true;
     } else if ([path isEqualToString:@"/nestedtop"]) {
-        expectHeaders(urlSchemeTask, true);
+        expectLegacyHeaders(urlSchemeTask, true);
         respond(urlSchemeTask, @"<iframe src='test://otherorigin/nestedmid'></iframe>");
     } else if ([path isEqualToString:@"/nestedmid"]) {
-        expectHeaders(urlSchemeTask, false);
+        expectLegacyHeaders(urlSchemeTask, false);
         respond(urlSchemeTask, @"<iframe src='test://toporigin/nestedbottom'></iframe>");
     } else if ([path isEqualToString:@"/nestedbottom"]) {
-        expectHeaders(urlSchemeTask, true);
+        expectLegacyHeaders(urlSchemeTask, true);
         respond(urlSchemeTask);
         thirdTestDone = true;
     } else if ([path isEqualToString:@"/requestfromaboutblank"]) {
-        expectHeaders(urlSchemeTask, true);
+        expectLegacyHeaders(urlSchemeTask, true);
         respond(urlSchemeTask);
         fourthTestDone = true;
-    } else
+    } else if ([path isEqualToString:@"/testcustomheaderfieldhosts"]) {
+        expectHeaders(urlSchemeTask, true);
+        NSString *html = @"<script>fetch('test://a.b.c.sub.hostwithasterisk.com/hosttest1',{mode:'no-cors'})"
+            ".then(function(response){fetch('test://subhostwithasterisk.com/hosttest2',{mode:'no-cors'})})"
+            ".then(function(response){fetch('test://hostwithoutasterisk.com/hosttest3',{mode:'no-cors'})})"
+            ".then(function(response){fetch('test://a.b.c.sub.hostwithoutasterisk.com/hosttest4',{mode:'no-cors'})})</script>";
+        respond(urlSchemeTask, html);
+    } else if ([path isEqualToString:@"/hosttest1"]) {
+        expectHeaders(urlSchemeTask, true);
+        respond(urlSchemeTask);
+    } else if ([path isEqualToString:@"/hosttest2"]) {
+        expectHeaders(urlSchemeTask, false);
+        respond(urlSchemeTask);
+    } else if ([path isEqualToString:@"/hosttest3"]) {
+        expectHeaders(urlSchemeTask, true);
+        respond(urlSchemeTask);
+    } else if ([path isEqualToString:@"/hosttest4"]) {
+        expectHeaders(urlSchemeTask, false);
+        respond(urlSchemeTask);
+        fifthTestDone = true;
+    } else if ([path isEqualToString:@"/testcustomheaderfieldhosts"])
         EXPECT_TRUE(false);
 }
 
@@ -1023,6 +1070,9 @@
 
     [webView loadRequest:[NSURLRequest requestWithURL:[NSURL URLWithString:@"test://toporigin/nestedtop"]]];
     TestWebKitAPI::Util::run(&thirdTestDone);
+
+    [webView loadRequest:[NSURLRequest requestWithURL:[NSURL URLWithString:@"test://host/testcustomheaderfieldhosts"]]];
+    TestWebKitAPI::Util::run(&fifthTestDone);
 }
 
 static unsigned loadCount;