diff --git a/Source/WTF/ChangeLog b/Source/WTF/ChangeLog
index 6efab37..16876d1 100644
--- a/Source/WTF/ChangeLog
+++ b/Source/WTF/ChangeLog
@@ -1,3 +1,13 @@
+2019-05-16  Alex Christensen  <achristensen@webkit.org>
+
+        Add a unit test for client certificate authentication
+        https://bugs.webkit.org/show_bug.cgi?id=197800
+
+        Reviewed by Youenn Fablet.
+
+        * wtf/spi/cocoa/SecuritySPI.h:
+        Move declarations from ArgumentCodersCF.cpp so they can be shared.
+
 2019-05-16  Eike Rathke  <erack@redhat.com>
 
         Fix memcpy() call for big endian
diff --git a/Source/WTF/wtf/spi/cocoa/SecuritySPI.h b/Source/WTF/wtf/spi/cocoa/SecuritySPI.h
index 96e30a7..9357d0c 100644
--- a/Source/WTF/wtf/spi/cocoa/SecuritySPI.h
+++ b/Source/WTF/wtf/spi/cocoa/SecuritySPI.h
@@ -27,7 +27,10 @@
 
 #if USE(APPLE_INTERNAL_SDK)
 
+#include <Security/SecAccessControlPriv.h>
 #include <Security/SecCertificatePriv.h>
+#include <Security/SecIdentityPriv.h>
+#include <Security/SecKeyPriv.h>
 #include <Security/SecTask.h>
 #include <Security/SecTrustPriv.h>
 
@@ -67,7 +70,11 @@
 
 SecTaskRef SecTaskCreateWithAuditToken(CFAllocatorRef, audit_token_t);
 SecTaskRef SecTaskCreateFromSelf(CFAllocatorRef);
-CFTypeRef SecTaskCopyValueForEntitlement(SecTaskRef, CFStringRef entitlement, CFErrorRef *);
+CFTypeRef SecTaskCopyValueForEntitlement(SecTaskRef, CFStringRef entitlement, CFErrorRef*);
+SecIdentityRef SecIdentityCreate(CFAllocatorRef, SecCertificateRef, SecKeyRef);
+OSStatus SecKeyFindWithPersistentRef(CFDataRef persistentRef, SecKeyRef* lookedUpData);
+SecAccessControlRef SecAccessControlCreateFromData(CFAllocatorRef, CFDataRef, CFErrorRef*);
+CFDataRef SecAccessControlCopyData(SecAccessControlRef);
 
 #if PLATFORM(MAC)
 #include <Security/SecAsn1Types.h>
diff --git a/Source/WebKit/ChangeLog b/Source/WebKit/ChangeLog
index 59b4370..f843850 100644
--- a/Source/WebKit/ChangeLog
+++ b/Source/WebKit/ChangeLog
@@ -1,5 +1,15 @@
 2019-05-16  Alex Christensen  <achristensen@webkit.org>
 
+        Add a unit test for client certificate authentication
+        https://bugs.webkit.org/show_bug.cgi?id=197800
+
+        Reviewed by Youenn Fablet.
+
+        * Shared/cf/ArgumentCodersCF.cpp:
+        Move SPI declarations to SecuritySPI.h.
+
+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
 
diff --git a/Source/WebKit/Shared/cf/ArgumentCodersCF.cpp b/Source/WebKit/Shared/cf/ArgumentCodersCF.cpp
index fdb8e88..d35925b 100644
--- a/Source/WebKit/Shared/cf/ArgumentCodersCF.cpp
+++ b/Source/WebKit/Shared/cf/ArgumentCodersCF.cpp
@@ -41,29 +41,6 @@
 #import <Foundation/Foundation.h>
 #endif
 
-#if USE(APPLE_INTERNAL_SDK)
-#include <Security/SecIdentityPriv.h>
-#endif
-
-extern "C" SecIdentityRef SecIdentityCreate(CFAllocatorRef allocator, SecCertificateRef certificate, SecKeyRef privateKey);
-
-#if PLATFORM(IOS_FAMILY)
-#if USE(APPLE_INTERNAL_SDK)
-#include <Security/SecKeyPriv.h>
-#endif
-
-extern "C" OSStatus SecKeyFindWithPersistentRef(CFDataRef persistentRef, SecKeyRef* lookedUpData);
-#endif
-
-#if HAVE(SEC_ACCESS_CONTROL)
-#if USE(APPLE_INTERNAL_SDK)
-#include <Security/SecAccessControlPriv.h>
-#endif
-
-extern "C" SecAccessControlRef SecAccessControlCreateFromData(CFAllocatorRef allocator, CFDataRef data, CFErrorRef *error);
-extern "C" CFDataRef SecAccessControlCopyData(SecAccessControlRef access_control);
-#endif
-
 namespace IPC {
 using namespace WebCore;
 
diff --git a/Tools/ChangeLog b/Tools/ChangeLog
index 80a3627..fe34eef 100644
--- a/Tools/ChangeLog
+++ b/Tools/ChangeLog
@@ -1,5 +1,44 @@
 2019-05-16  Alex Christensen  <achristensen@webkit.org>
 
+        Add a unit test for client certificate authentication
+        https://bugs.webkit.org/show_bug.cgi?id=197800
+
+        Reviewed by Youenn Fablet.
+
+        Make better abstractions for reading and writing from/to TCPServer.
+        Add a unit test that causes a client certificate authentication challenge to happen.
+
+        * TestWebKitAPI/TCPServer.cpp:
+        (TestWebKitAPI::TCPServer::TCPServer):
+        (TestWebKitAPI::TCPServer::read):
+        (TestWebKitAPI::TCPServer::write):
+        (TestWebKitAPI::TCPServer::respondWithChallengeThenOK):
+        (TestWebKitAPI::TCPServer::respondWithOK):
+        * TestWebKitAPI/TCPServer.h:
+        * TestWebKitAPI/Tests/WebKitCocoa/Challenge.mm:
+        (credentialWithIdentity):
+        (-[ChallengeDelegate webView:didReceiveAuthenticationChallenge:completionHandler:]):
+        (TEST):
+        (-[ClientCertificateDelegate webView:didFinishNavigation:]):
+        (-[ClientCertificateDelegate webView:didReceiveAuthenticationChallenge:completionHandler:]):
+        (-[ClientCertificateDelegate challengeCount]):
+        (TestWebKitAPI::TEST):
+        (respondWithChallengeThenOK): Deleted.
+        (credentialWithIdentityAndKeychainPath): Deleted.
+        * TestWebKitAPI/Tests/WebKitCocoa/PDFLinkReferrer.mm:
+        (TEST):
+        * TestWebKitAPI/Tests/WebKitCocoa/Proxy.mm:
+        (TestWebKitAPI::TEST):
+        * TestWebKitAPI/Tests/WebKitCocoa/WKNavigationResponse.mm:
+        (TEST):
+        (readRequest): Deleted.
+        (writeResponse): Deleted.
+        * TestWebKitAPI/Tests/WebKitCocoa/WKWebsiteDatastore.mm:
+        (TestWebKitAPI::TEST):
+        (TestWebKitAPI::respondWithChallengeThenOK): Deleted.
+
+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
 
diff --git a/Tools/TestWebKitAPI/TCPServer.cpp b/Tools/TestWebKitAPI/TCPServer.cpp
index 31b1470..2ba7a63 100644
--- a/Tools/TestWebKitAPI/TCPServer.cpp
+++ b/Tools/TestWebKitAPI/TCPServer.cpp
@@ -30,6 +30,7 @@
 #include <thread>
 #include <unistd.h>
 #include <wtf/Optional.h>
+#include <wtf/text/Base64.h>
 
 extern "C" {
 
@@ -38,6 +39,10 @@
 struct SSL_CTX;
 struct EVP_PKEY;
 struct SSL_METHOD;
+struct X509_STORE_CTX {
+    void* unused;
+    X509* cert;
+};
 struct pem_password_cb;
 int BIO_free(BIO*);
 int SSL_free(SSL*);
@@ -56,6 +61,15 @@
 SSL* SSL_new(SSL_CTX*);
 int SSL_accept(SSL*);
 int SSL_set_fd(SSL*, int);
+void SSL_CTX_set_verify(SSL_CTX*, int, int (*)(int, X509_STORE_CTX*));
+void SSL_CTX_set_cert_verify_callback(SSL_CTX*, int (*)(X509_STORE_CTX*, void*), void*);
+int SSL_get_error(const SSL*, int);
+int SSL_read(SSL*, void*, int);
+int SSL_write(SSL*, const void*, int);
+int i2d_X509(X509*, unsigned char**);
+void OPENSSL_free(void*);
+#define SSL_VERIFY_PEER 0x01
+#define SSL_VERIFY_FAIL_IF_NO_PEER_CERT 0x02
 
 } // extern "C"
 
@@ -92,6 +106,12 @@
         EVP_PKEY_free(key);
     }
 };
+template<> struct deleter<uint8_t[]> {
+    void operator()(uint8_t* buffer)
+    {
+        OPENSSL_free(buffer);
+    }
+};
 
 TCPServer::TCPServer(Function<void(Socket)>&& connectionHandler, size_t connections)
     : m_connectionHandler(WTFMove(connectionHandler))
@@ -101,7 +121,7 @@
 
 TCPServer::TCPServer(Protocol protocol, Function<void(SSL*)>&& secureConnectionHandler)
 {
-    auto startSecureConnection = [secureConnectionHandler = WTFMove(secureConnectionHandler)] (Socket socket) {
+    auto startSecureConnection = [secureConnectionHandler = WTFMove(secureConnectionHandler), protocol] (Socket socket) {
         SSL_library_init();
 
         std::unique_ptr<SSL_CTX, deleter<SSL_CTX>> ctx(SSL_CTX_new(SSLv23_server_method()));
@@ -129,6 +149,20 @@
         ASSERT(certX509);
         SSL_CTX_use_certificate(ctx.get(), certX509.get());
 
+        if (protocol == Protocol::HTTPSWithClientCertificateRequest) {
+            SSL_CTX_set_verify(ctx.get(), SSL_VERIFY_PEER | SSL_VERIFY_FAIL_IF_NO_PEER_CERT, nullptr);
+            SSL_CTX_set_cert_verify_callback(ctx.get(), [] (X509_STORE_CTX* store_ctx, void*) -> int {
+                uint8_t* bufferPointer = nullptr;
+                auto length = i2d_X509(store_ctx->cert, &bufferPointer);
+                std::unique_ptr<uint8_t[], deleter<uint8_t[]>> buffer(bufferPointer);
+                auto expectedCert = testCertificate();
+                EXPECT_EQ(static_cast<int>(expectedCert.size()), length);
+                for (int i = 0; i < length; ++i)
+                    EXPECT_EQ(buffer.get()[i], expectedCert[i]);
+                return 1;
+            }, nullptr);
+        }
+
         // This is a test key from BoringSSL.
         char kKeyPEM[] =
         "-----BEGIN RSA PRIVATE KEY-----\n"
@@ -164,6 +198,7 @@
 
     switch (protocol) {
     case Protocol::HTTPS:
+    case Protocol::HTTPSWithClientCertificateRequest:
         m_connectionHandler = WTFMove(startSecureConnection);
         break;
     case Protocol::HTTPSProxy:
@@ -239,4 +274,182 @@
     return WTF::nullopt;
 }
 
+template<> Vector<uint8_t> TCPServer::read(Socket socket)
+{
+    uint8_t buffer[1000];
+    auto bytesRead = ::read(socket, buffer, sizeof(buffer));
+    ASSERT_UNUSED(bytesRead, bytesRead > 0);
+    ASSERT(static_cast<size_t>(bytesRead) < sizeof(buffer));
+
+    Vector<uint8_t> vector;
+    vector.append(buffer, bytesRead);
+    return vector;
+}
+
+template<> void TCPServer::write(Socket socket, const void* response, size_t length)
+{
+    auto bytesWritten = ::write(socket, response, length);
+    EXPECT_EQ(static_cast<size_t>(bytesWritten), length);
+}
+
+template<> Vector<uint8_t> TCPServer::read(SSL* ssl)
+{
+    uint8_t buffer[1000];
+    auto bytesRead = SSL_read(ssl, buffer, sizeof(buffer));
+    ASSERT_UNUSED(bytesRead, bytesRead > 0);
+    ASSERT(static_cast<size_t>(bytesRead) < sizeof(buffer));
+
+    Vector<uint8_t> vector;
+    vector.append(buffer, bytesRead);
+    return vector;
+}
+
+template<> void TCPServer::write(SSL* ssl, const void* response, size_t length)
+{
+    auto bytesWritten = SSL_write(ssl, response, length);
+    EXPECT_EQ(static_cast<size_t>(bytesWritten), length);
+}
+
+void TCPServer::respondWithChallengeThenOK(Socket socket)
+{
+    read(socket);
+    
+    const char* challengeHeader =
+    "HTTP/1.1 401 Unauthorized\r\n"
+    "Date: Sat, 23 Mar 2019 06:29:01 GMT\r\n"
+    "Content-Length: 0\r\n"
+    "WWW-Authenticate: Basic realm=\"testrealm\"\r\n\r\n";
+    write(socket, challengeHeader, strlen(challengeHeader));
+    
+    read(socket);
+    
+    const char* responseHeader =
+    "HTTP/1.1 200 OK\r\n"
+    "Content-Length: 13\r\n\r\n"
+    "Hello, World!";
+    write(socket, responseHeader, strlen(responseHeader));
+}
+
+void TCPServer::respondWithOK(SSL* ssl)
+{
+    read(ssl);
+    
+    const char* reply = ""
+    "HTTP/1.1 200 OK\r\n"
+    "Content-Length: 34\r\n\r\n"
+    "<script>alert('success!')</script>";
+    write(ssl, reply, strlen(reply));
+}
+
+Vector<uint8_t> TCPServer::testCertificate()
+{
+    // Certificate and private key were generated by running this command:
+    // openssl req -x509 -newkey rsa:4096 -keyout key.pem -out cert.pem -days 365 -nodes
+    // and entering this information:
+    /*
+     Country Name (2 letter code) []:US
+     State or Province Name (full name) []:New Mexico
+     Locality Name (eg, city) []:Santa Fe
+     Organization Name (eg, company) []:Self
+     Organizational Unit Name (eg, section) []:Myself
+     Common Name (eg, fully qualified host name) []:Me
+     Email Address []:me@example.com
+     */
+    
+    String pemEncodedCertificate(""
+    "MIIFgDCCA2gCCQCKHiPRU5MQuDANBgkqhkiG9w0BAQsFADCBgTELMAkGA1UEBhMC"
+    "VVMxEzARBgNVBAgMCk5ldyBNZXhpY28xETAPBgNVBAcMCFNhbnRhIEZlMQ0wCwYD"
+    "VQQKDARTZWxmMQ8wDQYDVQQLDAZNeXNlbGYxCzAJBgNVBAMMAk1lMR0wGwYJKoZI"
+    "hvcNAQkBFg5tZUBleGFtcGxlLmNvbTAeFw0xOTAzMjMwNTUwMTRaFw0yMDAzMjIw"
+    "NTUwMTRaMIGBMQswCQYDVQQGEwJVUzETMBEGA1UECAwKTmV3IE1leGljbzERMA8G"
+    "A1UEBwwIU2FudGEgRmUxDTALBgNVBAoMBFNlbGYxDzANBgNVBAsMBk15c2VsZjEL"
+    "MAkGA1UEAwwCTWUxHTAbBgkqhkiG9w0BCQEWDm1lQGV4YW1wbGUuY29tMIICIjAN"
+    "BgkqhkiG9w0BAQEFAAOCAg8AMIICCgKCAgEA3rhN4SPg8VY/PtGDNKY3T9JISgby"
+    "8YGMJx0vO+YZFZm3G3fsTUsyvDyEHwqp5abCZRB/By1PwWkNrfxn/XP8P034JPlE"
+    "6irViuAYQrqUh6k7ZR8CpOM5GEcRZgAUJGGQwNlOkEwaHnMGc8SsHurgDPh5XBpg"
+    "bDytd7BJuB1NoI/KJmhcajkAuV3varS+uPLofPHNqe+cL8hNnjZQwHWarP45ks4e"
+    "BcOD7twqxuHnVm/FWErpY8Ws5s1MrPThUdDahjEMf+YfDJ9KL8y304yS8J8feCxY"
+    "fcH4BvgLtJmBNHJgj3eND/EMZjJgz2FsBjrJk8kKD31cw+4Wp8UF4skWXCf46+mN"
+    "OHp13PeSCZLyF4ZAHazUVknDPcc2YNrWVV1i6n3T15kI0T5Z7bstdmALuSkE2cuJ"
+    "SVNO6gR+ZsVRTneuQxwWTU0MNEhAPFOX2BhGP5eisgEUzknxMJddFDn9Wxklu1Jh"
+    "gkzASA/+3AmlrFZMPhOhjEul0zjgNR5RBl1G8Hz92LAx5UEDBtdLg71I+I8AzQOh"
+    "d6LtBekECxA16pSappg5vcW9Z/8N6ZlsHnZ2FztA0nCOflkoO9iejOpcuFN4EVYD"
+    "xItwctKw1LCeND/s4kmoRRnXbX7k9O6cI1UUWM595Gsu5tPa33M5AZFCav2gOVuY"
+    "djppS0HOfo5hv6cCAwEAATANBgkqhkiG9w0BAQsFAAOCAgEAY8EWaAFEfw7OV+oD"
+    "XUZSIYXq3EH2E5p3q38AhIOLRjBuB+utyu7Q6rxMMHuw2TtsN+zbAR7yrjfsseA3"
+    "4TM1xe4Nk7NVNHRoZQ+C0Iqf9fvcioMvT1tTrma0MhKSjFQpx+PvyLVbD7YdP86L"
+    "meehKqU7h1pLGAiGwjoaZ9Ybh6Kuq/MTAHy3D8+wk7B36VBxF6diVlUPZJZQWKJy"
+    "MKy9G3sze1ZGt9WeE0AMvkN2HIef0HTKCUZ3eBvecOMijxL0WhWo5Qyf5k6ylCaU"
+    "2fx+M8DfDcwFo7tSgLxSK3GCFpxPfiDt6Qk8c9tQn5S1gY3t6LJuwVCFwUIXlNkB"
+    "JD7+cZ1Z/tCrEhzj3YCk0uUU8CifoU+4FG+HGFP+SPztsYE055mSj3+Esh+oyoVB"
+    "gBH90sE2T1i0eNI8f61oSgwYFeHsf7fC71XEXLFR+GwNdmwqlmwlDZEpTu7BoNN+"
+    "q7+Tfk1MRkJlL1PH6Yu/IPhZiNh4tyIqDOtlYfzp577A+OUU+q5PPRFRIsqheOxt"
+    "mNlHx4Uzd4U3ITfmogJazjqwYO2viBZY4jUQmyZs75eH/jiUFHWRsha3AdnW5LWa"
+    "G3PFnYbW8urH0NSJG/W+/9DA+Y7Aa0cs4TPpuBGZ0NU1W94OoCMo4lkO6H/y6Leu"
+    "3vjZD3y9kZk7mre9XHwkI8MdK5s=");
+    
+    Vector<uint8_t> vector;
+    base64Decode(pemEncodedCertificate, vector, WTF::Base64DecodeOptions::Base64Default);
+    return vector;
+}
+
+Vector<uint8_t> TCPServer::testPrivateKey()
+{
+    String pemEncodedPrivateKey(""
+    "MIIJQgIBADANBgkqhkiG9w0BAQEFAASCCSwwggkoAgEAAoICAQDeuE3hI+DxVj8+"
+    "0YM0pjdP0khKBvLxgYwnHS875hkVmbcbd+xNSzK8PIQfCqnlpsJlEH8HLU/BaQ2t"
+    "/Gf9c/w/Tfgk+UTqKtWK4BhCupSHqTtlHwKk4zkYRxFmABQkYZDA2U6QTBoecwZz"
+    "xKwe6uAM+HlcGmBsPK13sEm4HU2gj8omaFxqOQC5Xe9qtL648uh88c2p75wvyE2e"
+    "NlDAdZqs/jmSzh4Fw4Pu3CrG4edWb8VYSuljxazmzUys9OFR0NqGMQx/5h8Mn0ov"
+    "zLfTjJLwnx94LFh9wfgG+Au0mYE0cmCPd40P8QxmMmDPYWwGOsmTyQoPfVzD7han"
+    "xQXiyRZcJ/jr6Y04enXc95IJkvIXhkAdrNRWScM9xzZg2tZVXWLqfdPXmQjRPlnt"
+    "uy12YAu5KQTZy4lJU07qBH5mxVFOd65DHBZNTQw0SEA8U5fYGEY/l6KyARTOSfEw"
+    "l10UOf1bGSW7UmGCTMBID/7cCaWsVkw+E6GMS6XTOOA1HlEGXUbwfP3YsDHlQQMG"
+    "10uDvUj4jwDNA6F3ou0F6QQLEDXqlJqmmDm9xb1n/w3pmWwednYXO0DScI5+WSg7"
+    "2J6M6ly4U3gRVgPEi3By0rDUsJ40P+ziSahFGddtfuT07pwjVRRYzn3kay7m09rf"
+    "czkBkUJq/aA5W5h2OmlLQc5+jmG/pwIDAQABAoICAGra/Cp/f0Xqvk9ST+Prt2/p"
+    "kNtLeDXclLSTcP0JCZHufQaFw+7VnFLpqe4GvLq9Bllcz8VOvQwrbe/CwNW+VxC8"
+    "RMjge2rqACgwGhOx1t87l46NkUQw7Ey0lCle8kr+MGgGGoZqrMFdKIRUoMv4nmQ6"
+    "tmc1FHv5pLRe9Q+Lp5nYQwGoYmZoUOueoOaOL08m49pGXQkiN8pJDMxSfO3Jvtsu"
+    "4cqIb6kOQ/dO1Is1CTvURld1IYLH7YuShi4ZEx2g2ac2Uyvt6YmxxvMmAjBSKpGd"
+    "loiepho3/NrDGUKdv3q9QYyzrA8w9GT32LDGqgBXJi1scBI8cExkp6P4iDllhv7s"
+    "vZsspvobRJa3O1zk863LHXa24JCnyuzimqezZ2Olh7l4olHoYD6UFC9jfd4KcHRg"
+    "1c4syqt/n8AK/1s1eBfS9dzb5Cfjt9MtKYslxvLzq1WwOINwz8rIYuRi0PcLm9hs"
+    "l+U0u/zB37eMgv6+iwDXk1fSjbuYsE/bETWYknKGNFFL5JSiKV7WCpmgNTTrrE4K"
+    "S8E6hR9uPOAaow7vPCCt4xLX/48l2EI6Zeq6qOpq1lJ2qcy8r4tyuQgNRLQMkZg1"
+    "AxQl6vnQ8Cu4iu+NIhef0y9Z7qkfNvZeCj5GlFB9c2YjV8Y2mdWfJB4qWK3Z/+MJ"
+    "QOTCKRz7/LxLNBUepRjJAoIBAQD3ZsV5tWU9ZSKcVJ9DC7TZk0P+lhcisZr0nL0t"
+    "PQuQO+pHvPI1MqRnNskHJhyPnqVCi+dp89tK/It590ULl8os6UC1FhytBPoT1YPd"
+    "WGWep2pOc7bVpi4ip31y+ImfgeZyJtMATdme3kBPAOe5NGE9Gig/l5nqLyb02sd1"
+    "QW7O0GdqLx3DpLw4SLlhMf6aE0uGRS8sfB085e4DGn54O2wEVuSZqZl5NNEf35Rz"
+    "Xgim3h+RWF1ZFSQzjB/smN0Zh+v3Iz7vEJ1h0ywV6o+GzvHkP9HE6gLIhtyV8OEw"
+    "vlyYk1Ga7pUVGRh8o8OMe6RR9DQi7JqC4eI7GckmBzaqzJcDAoIBAQDmde6ATew3"
+    "H9bQK6xnbMIncz/COpIISdlcFb23AHGEb4b4VhJFBNwxrNL6tHKSFLeYZFLhTdhx"
+    "PfXyULHNf5ozdEkl0WrleroDdogbCyWg5uJp9/Q68sbwbGr8CAlO7ZHYTrjuQf1K"
+    "AS9pCm77KP3k2d3UlG+pelDjXLoBziXq0NjxJpMz45vrIx8rSWzFNjMGjXT3fXaS"
+    "962k/0AXei5/bfuhBxlm7Pni0bQJIWFkeaUuGlrOaHDRxUiX1r9IZS9wv5lk1Ptg"
+    "idpbcWyw18cFGTvjdKhRbZH8EsbmzmNNsCGdgCMqFkKYsW16QKoCj/NAovI3n0qn"
+    "6VoRa0sGmTGNAoIBACl/mqZEsBuxSDHy29gSMZ7BXglpQa43HmfjlrPs5nCmLDEm"
+    "V3Zm7T7G6MeDNA0/LjdQYlvaZLFaVUb7HCDKsEYCRjFZ6St4hz4mdXz+Y+VN7b4F"
+    "GOkTe++iKp/LYsJXtsD1FDWb2WIVo7Hc1AGz8I+gQJoSIuYuTJmLzSM0+5JDUOV1"
+    "y8dSbaP/RuEv0qYjkGqQVk5e70SUyOzKV+ZxCThdHvFLiovTOTTgevUzE75xydfG"
+    "e7oCmtTurzgvl/69Vu5Ygij1n4CWPHHcq4CQW/DOZ7BhFGBwhrW79voHJF8PbwPO"
+    "+0DTudDGY3nAD5sTnF8zUuObYihJtfzj/t59fOMCggEBAIYuuBUASb62zQ4bv5/g"
+    "VRM/KSpfi9NDnEjfZ7x7h5zCiuVgx/ZjpAlQRO8vzV18roEOOKtx9cnJd8AEd+Hc"
+    "n93BoS1hx0mhsVh+1TRZwyjyBXYJpqwD2wz1Mz1XOIQ6EqbM/yPKTD2gfwg7yO53"
+    "qYxrxZsWagVVcG9Q+ARBERatTwLpoN+fcJLxuh4r/Ca/LepsxmOrKzTa/MGK1LhW"
+    "rWgIk2/ogEPLSptj2d1PEDO+GAzFz4VKjhW1NlUh9fGi6IJPLHLnBw3odbi0S8KT"
+    "gA9Z5+LBc5clotAP5rtQA8Wh/ZCEoPTKTTA2bjW2HMatJcbGmR0FpCQr3AM0Y1SO"
+    "MakCggEALru6QZ6YUwJJG45H1eq/rPdDY8tqqjJVViKoBVvzKj/XfJZYEVQiIw5p"
+    "uoGhDoyFuFUeIh/d1Jc2Iruy2WjoOkiQYtIugDHHxRrkLdQcjPhlCTCE/mmySJt+"
+    "bkUbiHIbQ8dJ5yj8SKr0bHzqEtOy9/JeRjkYGHC6bVWpq5FA2MBhf4dNjJ4UDlnT"
+    "vuePcTjr7nnfY1sztvfVl9D8dmgT+TBnOOV6yWj1gm5bS1DxQSLgNmtKxJ8tAh2u"
+    "dEObvcpShP22ItOVjSampRuAuRG26ZemEbGCI3J6Mqx3y6m+6HwultsgtdzDgrFe"
+    "qJfU8bbdbu2pi47Y4FdJK0HLffl5Rw==");
+
+    Vector<uint8_t> vector;
+    base64Decode(pemEncodedPrivateKey, vector, WTF::Base64DecodeOptions::Base64Default);
+    return vector;
+}
+    
 } // namespace TestWebKitAPI
diff --git a/Tools/TestWebKitAPI/TCPServer.h b/Tools/TestWebKitAPI/TCPServer.h
index fbe81a2..6668c73 100644
--- a/Tools/TestWebKitAPI/TCPServer.h
+++ b/Tools/TestWebKitAPI/TCPServer.h
@@ -29,11 +29,7 @@
 #include <wtf/Function.h>
 #include <wtf/Vector.h>
 
-extern "C" {
 struct SSL;
-int SSL_read(SSL*, void*, int);
-int SSL_write(SSL*, const void*, int);
-}
 
 namespace TestWebKitAPI {
 
@@ -44,14 +40,25 @@
     static constexpr Port InvalidPort = 0;
     
     TCPServer(Function<void(Socket)>&&, size_t connections = 1);
-    enum class Protocol : bool {
-        HTTPS, HTTPSProxy
+    enum class Protocol : uint8_t {
+        HTTPS,
+        HTTPSProxy,
+        HTTPSWithClientCertificateRequest,
     };
     TCPServer(Protocol, Function<void(SSL*)>&&);
     ~TCPServer();
     
     Port port() const { return m_port; }
     
+    static void respondWithOK(SSL*);
+    static void respondWithChallengeThenOK(Socket);
+
+    template<typename T> static Vector<uint8_t> read(T);
+    template<typename T> static void write(T, const void*, size_t);
+
+    static Vector<uint8_t> testPrivateKey();
+    static Vector<uint8_t> testCertificate();
+    
 private:
     Optional<Socket> socketBindListen(size_t connections);
     void listenForConnections(size_t connections);
diff --git a/Tools/TestWebKitAPI/Tests/WebKitCocoa/Challenge.mm b/Tools/TestWebKitAPI/Tests/WebKitCocoa/Challenge.mm
index 816afb5..a34e69e 100644
--- a/Tools/TestWebKitAPI/Tests/WebKitCocoa/Challenge.mm
+++ b/Tools/TestWebKitAPI/Tests/WebKitCocoa/Challenge.mm
@@ -33,141 +33,17 @@
 #import <WebKit/WKProcessPoolPrivate.h>
 #import <WebKit/WKWebsiteDataRecordPrivate.h>
 #import <wtf/RetainPtr.h>
+#import <wtf/spi/cocoa/SecuritySPI.h>
 
 static bool navigationFinished;
 
-static void respondWithChallengeThenOK(int socket)
+static RetainPtr<NSURLCredential> credentialWithIdentity()
 {
-    char readBuffer[1000];
-    auto bytesRead = ::read(socket, readBuffer, sizeof(readBuffer));
-    EXPECT_GT(bytesRead, 0);
-    EXPECT_TRUE(static_cast<size_t>(bytesRead) < sizeof(readBuffer));
+    auto certificateBytes = TestWebKitAPI::TCPServer::testCertificate();
+    auto certificate = adoptCF(SecCertificateCreateWithData(nullptr, (__bridge CFDataRef)[NSData dataWithBytes:certificateBytes.data() length:certificateBytes.size()]));
     
-    const char* challengeHeader =
-    "HTTP/1.1 401 Unauthorized\r\n"
-    "Date: Sat, 23 Mar 2019 06:29:01 GMT\r\n"
-    "Content-Length: 0\r\n"
-    "WWW-Authenticate: Basic realm=\"testrealm\"\r\n\r\n";
-    auto bytesWritten = ::write(socket, challengeHeader, strlen(challengeHeader));
-    EXPECT_EQ(static_cast<size_t>(bytesWritten), strlen(challengeHeader));
-    
-    bytesRead = ::read(socket, readBuffer, sizeof(readBuffer));
-    EXPECT_GT(bytesRead, 0);
-    EXPECT_TRUE(static_cast<size_t>(bytesRead) < sizeof(readBuffer));
-    
-    const char* responseHeader =
-    "HTTP/1.1 200 OK\r\n"
-    "Content-Length: 13\r\n\r\n"
-    "Hello, World!";
-    bytesWritten = ::write(socket, responseHeader, strlen(responseHeader));
-    EXPECT_EQ(static_cast<size_t>(bytesWritten), strlen(responseHeader));
-}
-
-#if PLATFORM(MAC)
-
-static std::pair<RetainPtr<NSURLCredential>, RetainPtr<NSString>> credentialWithIdentityAndKeychainPath()
-{
-    // Certificate and private key were generated by running this command:
-    // openssl req -x509 -newkey rsa:4096 -keyout key.pem -out cert.pem -days 365 -nodes
-    // and entering this information:
-    /*
-     Country Name (2 letter code) []:US
-     State or Province Name (full name) []:New Mexico
-     Locality Name (eg, city) []:Santa Fe
-     Organization Name (eg, company) []:Self
-     Organizational Unit Name (eg, section) []:Myself
-     Common Name (eg, fully qualified host name) []:Me
-     Email Address []:me@example.com
-     */
-    
-    NSString *pemEncodedCertificate = @""
-    "MIIFgDCCA2gCCQCKHiPRU5MQuDANBgkqhkiG9w0BAQsFADCBgTELMAkGA1UEBhMC"
-    "VVMxEzARBgNVBAgMCk5ldyBNZXhpY28xETAPBgNVBAcMCFNhbnRhIEZlMQ0wCwYD"
-    "VQQKDARTZWxmMQ8wDQYDVQQLDAZNeXNlbGYxCzAJBgNVBAMMAk1lMR0wGwYJKoZI"
-    "hvcNAQkBFg5tZUBleGFtcGxlLmNvbTAeFw0xOTAzMjMwNTUwMTRaFw0yMDAzMjIw"
-    "NTUwMTRaMIGBMQswCQYDVQQGEwJVUzETMBEGA1UECAwKTmV3IE1leGljbzERMA8G"
-    "A1UEBwwIU2FudGEgRmUxDTALBgNVBAoMBFNlbGYxDzANBgNVBAsMBk15c2VsZjEL"
-    "MAkGA1UEAwwCTWUxHTAbBgkqhkiG9w0BCQEWDm1lQGV4YW1wbGUuY29tMIICIjAN"
-    "BgkqhkiG9w0BAQEFAAOCAg8AMIICCgKCAgEA3rhN4SPg8VY/PtGDNKY3T9JISgby"
-    "8YGMJx0vO+YZFZm3G3fsTUsyvDyEHwqp5abCZRB/By1PwWkNrfxn/XP8P034JPlE"
-    "6irViuAYQrqUh6k7ZR8CpOM5GEcRZgAUJGGQwNlOkEwaHnMGc8SsHurgDPh5XBpg"
-    "bDytd7BJuB1NoI/KJmhcajkAuV3varS+uPLofPHNqe+cL8hNnjZQwHWarP45ks4e"
-    "BcOD7twqxuHnVm/FWErpY8Ws5s1MrPThUdDahjEMf+YfDJ9KL8y304yS8J8feCxY"
-    "fcH4BvgLtJmBNHJgj3eND/EMZjJgz2FsBjrJk8kKD31cw+4Wp8UF4skWXCf46+mN"
-    "OHp13PeSCZLyF4ZAHazUVknDPcc2YNrWVV1i6n3T15kI0T5Z7bstdmALuSkE2cuJ"
-    "SVNO6gR+ZsVRTneuQxwWTU0MNEhAPFOX2BhGP5eisgEUzknxMJddFDn9Wxklu1Jh"
-    "gkzASA/+3AmlrFZMPhOhjEul0zjgNR5RBl1G8Hz92LAx5UEDBtdLg71I+I8AzQOh"
-    "d6LtBekECxA16pSappg5vcW9Z/8N6ZlsHnZ2FztA0nCOflkoO9iejOpcuFN4EVYD"
-    "xItwctKw1LCeND/s4kmoRRnXbX7k9O6cI1UUWM595Gsu5tPa33M5AZFCav2gOVuY"
-    "djppS0HOfo5hv6cCAwEAATANBgkqhkiG9w0BAQsFAAOCAgEAY8EWaAFEfw7OV+oD"
-    "XUZSIYXq3EH2E5p3q38AhIOLRjBuB+utyu7Q6rxMMHuw2TtsN+zbAR7yrjfsseA3"
-    "4TM1xe4Nk7NVNHRoZQ+C0Iqf9fvcioMvT1tTrma0MhKSjFQpx+PvyLVbD7YdP86L"
-    "meehKqU7h1pLGAiGwjoaZ9Ybh6Kuq/MTAHy3D8+wk7B36VBxF6diVlUPZJZQWKJy"
-    "MKy9G3sze1ZGt9WeE0AMvkN2HIef0HTKCUZ3eBvecOMijxL0WhWo5Qyf5k6ylCaU"
-    "2fx+M8DfDcwFo7tSgLxSK3GCFpxPfiDt6Qk8c9tQn5S1gY3t6LJuwVCFwUIXlNkB"
-    "JD7+cZ1Z/tCrEhzj3YCk0uUU8CifoU+4FG+HGFP+SPztsYE055mSj3+Esh+oyoVB"
-    "gBH90sE2T1i0eNI8f61oSgwYFeHsf7fC71XEXLFR+GwNdmwqlmwlDZEpTu7BoNN+"
-    "q7+Tfk1MRkJlL1PH6Yu/IPhZiNh4tyIqDOtlYfzp577A+OUU+q5PPRFRIsqheOxt"
-    "mNlHx4Uzd4U3ITfmogJazjqwYO2viBZY4jUQmyZs75eH/jiUFHWRsha3AdnW5LWa"
-    "G3PFnYbW8urH0NSJG/W+/9DA+Y7Aa0cs4TPpuBGZ0NU1W94OoCMo4lkO6H/y6Leu"
-    "3vjZD3y9kZk7mre9XHwkI8MdK5s=";
-    
-    NSString *pemEncodedPrivateKey = @""
-    "MIIJQgIBADANBgkqhkiG9w0BAQEFAASCCSwwggkoAgEAAoICAQDeuE3hI+DxVj8+"
-    "0YM0pjdP0khKBvLxgYwnHS875hkVmbcbd+xNSzK8PIQfCqnlpsJlEH8HLU/BaQ2t"
-    "/Gf9c/w/Tfgk+UTqKtWK4BhCupSHqTtlHwKk4zkYRxFmABQkYZDA2U6QTBoecwZz"
-    "xKwe6uAM+HlcGmBsPK13sEm4HU2gj8omaFxqOQC5Xe9qtL648uh88c2p75wvyE2e"
-    "NlDAdZqs/jmSzh4Fw4Pu3CrG4edWb8VYSuljxazmzUys9OFR0NqGMQx/5h8Mn0ov"
-    "zLfTjJLwnx94LFh9wfgG+Au0mYE0cmCPd40P8QxmMmDPYWwGOsmTyQoPfVzD7han"
-    "xQXiyRZcJ/jr6Y04enXc95IJkvIXhkAdrNRWScM9xzZg2tZVXWLqfdPXmQjRPlnt"
-    "uy12YAu5KQTZy4lJU07qBH5mxVFOd65DHBZNTQw0SEA8U5fYGEY/l6KyARTOSfEw"
-    "l10UOf1bGSW7UmGCTMBID/7cCaWsVkw+E6GMS6XTOOA1HlEGXUbwfP3YsDHlQQMG"
-    "10uDvUj4jwDNA6F3ou0F6QQLEDXqlJqmmDm9xb1n/w3pmWwednYXO0DScI5+WSg7"
-    "2J6M6ly4U3gRVgPEi3By0rDUsJ40P+ziSahFGddtfuT07pwjVRRYzn3kay7m09rf"
-    "czkBkUJq/aA5W5h2OmlLQc5+jmG/pwIDAQABAoICAGra/Cp/f0Xqvk9ST+Prt2/p"
-    "kNtLeDXclLSTcP0JCZHufQaFw+7VnFLpqe4GvLq9Bllcz8VOvQwrbe/CwNW+VxC8"
-    "RMjge2rqACgwGhOx1t87l46NkUQw7Ey0lCle8kr+MGgGGoZqrMFdKIRUoMv4nmQ6"
-    "tmc1FHv5pLRe9Q+Lp5nYQwGoYmZoUOueoOaOL08m49pGXQkiN8pJDMxSfO3Jvtsu"
-    "4cqIb6kOQ/dO1Is1CTvURld1IYLH7YuShi4ZEx2g2ac2Uyvt6YmxxvMmAjBSKpGd"
-    "loiepho3/NrDGUKdv3q9QYyzrA8w9GT32LDGqgBXJi1scBI8cExkp6P4iDllhv7s"
-    "vZsspvobRJa3O1zk863LHXa24JCnyuzimqezZ2Olh7l4olHoYD6UFC9jfd4KcHRg"
-    "1c4syqt/n8AK/1s1eBfS9dzb5Cfjt9MtKYslxvLzq1WwOINwz8rIYuRi0PcLm9hs"
-    "l+U0u/zB37eMgv6+iwDXk1fSjbuYsE/bETWYknKGNFFL5JSiKV7WCpmgNTTrrE4K"
-    "S8E6hR9uPOAaow7vPCCt4xLX/48l2EI6Zeq6qOpq1lJ2qcy8r4tyuQgNRLQMkZg1"
-    "AxQl6vnQ8Cu4iu+NIhef0y9Z7qkfNvZeCj5GlFB9c2YjV8Y2mdWfJB4qWK3Z/+MJ"
-    "QOTCKRz7/LxLNBUepRjJAoIBAQD3ZsV5tWU9ZSKcVJ9DC7TZk0P+lhcisZr0nL0t"
-    "PQuQO+pHvPI1MqRnNskHJhyPnqVCi+dp89tK/It590ULl8os6UC1FhytBPoT1YPd"
-    "WGWep2pOc7bVpi4ip31y+ImfgeZyJtMATdme3kBPAOe5NGE9Gig/l5nqLyb02sd1"
-    "QW7O0GdqLx3DpLw4SLlhMf6aE0uGRS8sfB085e4DGn54O2wEVuSZqZl5NNEf35Rz"
-    "Xgim3h+RWF1ZFSQzjB/smN0Zh+v3Iz7vEJ1h0ywV6o+GzvHkP9HE6gLIhtyV8OEw"
-    "vlyYk1Ga7pUVGRh8o8OMe6RR9DQi7JqC4eI7GckmBzaqzJcDAoIBAQDmde6ATew3"
-    "H9bQK6xnbMIncz/COpIISdlcFb23AHGEb4b4VhJFBNwxrNL6tHKSFLeYZFLhTdhx"
-    "PfXyULHNf5ozdEkl0WrleroDdogbCyWg5uJp9/Q68sbwbGr8CAlO7ZHYTrjuQf1K"
-    "AS9pCm77KP3k2d3UlG+pelDjXLoBziXq0NjxJpMz45vrIx8rSWzFNjMGjXT3fXaS"
-    "962k/0AXei5/bfuhBxlm7Pni0bQJIWFkeaUuGlrOaHDRxUiX1r9IZS9wv5lk1Ptg"
-    "idpbcWyw18cFGTvjdKhRbZH8EsbmzmNNsCGdgCMqFkKYsW16QKoCj/NAovI3n0qn"
-    "6VoRa0sGmTGNAoIBACl/mqZEsBuxSDHy29gSMZ7BXglpQa43HmfjlrPs5nCmLDEm"
-    "V3Zm7T7G6MeDNA0/LjdQYlvaZLFaVUb7HCDKsEYCRjFZ6St4hz4mdXz+Y+VN7b4F"
-    "GOkTe++iKp/LYsJXtsD1FDWb2WIVo7Hc1AGz8I+gQJoSIuYuTJmLzSM0+5JDUOV1"
-    "y8dSbaP/RuEv0qYjkGqQVk5e70SUyOzKV+ZxCThdHvFLiovTOTTgevUzE75xydfG"
-    "e7oCmtTurzgvl/69Vu5Ygij1n4CWPHHcq4CQW/DOZ7BhFGBwhrW79voHJF8PbwPO"
-    "+0DTudDGY3nAD5sTnF8zUuObYihJtfzj/t59fOMCggEBAIYuuBUASb62zQ4bv5/g"
-    "VRM/KSpfi9NDnEjfZ7x7h5zCiuVgx/ZjpAlQRO8vzV18roEOOKtx9cnJd8AEd+Hc"
-    "n93BoS1hx0mhsVh+1TRZwyjyBXYJpqwD2wz1Mz1XOIQ6EqbM/yPKTD2gfwg7yO53"
-    "qYxrxZsWagVVcG9Q+ARBERatTwLpoN+fcJLxuh4r/Ca/LepsxmOrKzTa/MGK1LhW"
-    "rWgIk2/ogEPLSptj2d1PEDO+GAzFz4VKjhW1NlUh9fGi6IJPLHLnBw3odbi0S8KT"
-    "gA9Z5+LBc5clotAP5rtQA8Wh/ZCEoPTKTTA2bjW2HMatJcbGmR0FpCQr3AM0Y1SO"
-    "MakCggEALru6QZ6YUwJJG45H1eq/rPdDY8tqqjJVViKoBVvzKj/XfJZYEVQiIw5p"
-    "uoGhDoyFuFUeIh/d1Jc2Iruy2WjoOkiQYtIugDHHxRrkLdQcjPhlCTCE/mmySJt+"
-    "bkUbiHIbQ8dJ5yj8SKr0bHzqEtOy9/JeRjkYGHC6bVWpq5FA2MBhf4dNjJ4UDlnT"
-    "vuePcTjr7nnfY1sztvfVl9D8dmgT+TBnOOV6yWj1gm5bS1DxQSLgNmtKxJ8tAh2u"
-    "dEObvcpShP22ItOVjSampRuAuRG26ZemEbGCI3J6Mqx3y6m+6HwultsgtdzDgrFe"
-    "qJfU8bbdbu2pi47Y4FdJK0HLffl5Rw==";
-    
-    NSData *derEncodedCertificate = [[[NSData alloc] initWithBase64EncodedString:pemEncodedCertificate options:0] autorelease];
-    RetainPtr<SecCertificateRef> certificate = adoptCF(SecCertificateCreateWithData(nullptr, (__bridge CFDataRef)derEncodedCertificate));
-    
-    NSData *derEncodedPrivateKey = [[[NSData alloc] initWithBase64EncodedString:pemEncodedPrivateKey options:0] autorelease];
+    auto privateKeyBytes = TestWebKitAPI::TCPServer::testPrivateKey();
+    NSData *derEncodedPrivateKey = [NSData dataWithBytes:privateKeyBytes.data() length:privateKeyBytes.size()];
     NSDictionary* options = @{
         (id)kSecAttrKeyType: (id)kSecAttrKeyTypeRSA,
         (id)kSecAttrKeyClass: (id)kSecAttrKeyClassPrivate,
@@ -175,36 +51,16 @@
     };
     const NSUInteger pemEncodedPrivateKeyHeaderLength = 26;
     CFErrorRef error = nullptr;
-    RetainPtr<SecKeyRef> privateKey = adoptCF(SecKeyCreateWithData((__bridge CFDataRef)[derEncodedPrivateKey subdataWithRange:NSMakeRange(pemEncodedPrivateKeyHeaderLength, derEncodedPrivateKey.length - pemEncodedPrivateKeyHeaderLength)], (__bridge CFDictionaryRef)options, &error));
+    auto privateKey = adoptCF(SecKeyCreateWithData((__bridge CFDataRef)[derEncodedPrivateKey subdataWithRange:NSMakeRange(pemEncodedPrivateKeyHeaderLength, derEncodedPrivateKey.length - pemEncodedPrivateKeyHeaderLength)], (__bridge CFDictionaryRef)options, &error));
     EXPECT_NULL(error);
     EXPECT_NOT_NULL(privateKey.get());
 
-    SecKeychainRef keychainRef = nullptr;
-    const char* keychainPassword = "testpassword";
-    NSString *keychainPath = [NSTemporaryDirectory() stringByAppendingPathComponent:@"TestKeychain"];
-    OSStatus status = SecKeychainCreate([keychainPath UTF8String], strlen(keychainPassword), keychainPassword, NO, nullptr, &keychainRef);
-    EXPECT_TRUE(status == errSecSuccess);
-    RetainPtr<SecKeychainRef> keychain = adoptCF(keychainRef);
-    EXPECT_NOT_NULL(keychain);
-
-    SecExternalItemType type = kSecItemTypePrivateKey;
-    status = SecItemImport((__bridge CFDataRef)derEncodedPrivateKey, nullptr, nullptr, &type, 0, nullptr, keychain.get(), nullptr);
-    EXPECT_TRUE(status == errSecSuccess);
-
-    SecIdentityRef identityRef = nullptr;
-    status = SecIdentityCreateWithCertificate(keychain.get(), certificate.get(), &identityRef);
-    EXPECT_NOT_NULL(identityRef);
-    EXPECT_TRUE(status == errSecSuccess);
-    RetainPtr<SecIdentityRef> identity = adoptCF(identityRef);
+    auto identity = adoptCF(SecIdentityCreate(kCFAllocatorDefault, certificate.get(), privateKey.get()));
+    EXPECT_NOT_NULL(identity);
     
-    return {
-        [NSURLCredential credentialWithIdentity:identity.get() certificates:@[(id)certificate.get()] persistence:NSURLCredentialPersistenceNone],
-        keychainPath
-    };
+    return [NSURLCredential credentialWithIdentity:identity.get() certificates:@[(id)certificate.get()] persistence:NSURLCredentialPersistenceNone];
 }
 
-static RetainPtr<NSString> keychainPath;
-
 @interface ChallengeDelegate : NSObject <WKNavigationDelegate>
 @end
 
@@ -229,18 +85,15 @@
     EXPECT_TRUE([protectionSpace.authenticationMethod isEqualToString:NSURLAuthenticationMethodHTTPBasic]);
     EXPECT_EQ([(NSHTTPURLResponse *)challenge.failureResponse statusCode], 401);
 
-    auto pair = credentialWithIdentityAndKeychainPath();
-    completionHandler(NSURLSessionAuthChallengeUseCredential, pair.first.get());
-    keychainPath = WTFMove(pair.second);
+    completionHandler(NSURLSessionAuthChallengeUseCredential, credentialWithIdentity().get());
 }
 
 @end
 
-namespace TestWebKitAPI {
-
 TEST(Challenge, SecIdentity)
 {
-    TCPServer server(respondWithChallengeThenOK);
+    using namespace TestWebKitAPI;
+    TCPServer server(TCPServer::respondWithChallengeThenOK);
 
     auto webView = adoptNS([WKWebView new]);
     auto delegate = adoptNS([ChallengeDelegate new]);
@@ -248,15 +101,56 @@
     [webView loadRequest:[NSURLRequest requestWithURL:[NSURL URLWithString:[NSString stringWithFormat:@"http://127.0.0.1:%d/", server.port()]]]];
 
     Util::run(&navigationFinished);
-    
-    EXPECT_NOT_NULL(keychainPath.get());
-    NSError *error = nil;
-    [[NSFileManager defaultManager] removeItemAtPath:keychainPath.get() error:&error];
-    EXPECT_NULL(error);
 }
 
-} // namespace TestWebKitAPI
+@interface ClientCertificateDelegate : NSObject <WKNavigationDelegate> {
+    Vector<RetainPtr<NSString>> _authenticationMethods;
+}
+- (const Vector<RetainPtr<NSString>>&)authenticationMethods;
+@end
 
+@implementation ClientCertificateDelegate
+
+- (void)webView:(WKWebView *)webView didFinishNavigation:(null_unspecified WKNavigation *)navigation
+{
+    navigationFinished = true;
+}
+
+- (void)webView:(WKWebView *)webView didReceiveAuthenticationChallenge:(NSURLAuthenticationChallenge *)challenge completionHandler:(void (^)(NSURLSessionAuthChallengeDisposition, NSURLCredential *))completionHandler
+{
+    _authenticationMethods.append(challenge.protectionSpace.authenticationMethod);
+
+    if ([challenge.protectionSpace.authenticationMethod isEqualToString:NSURLAuthenticationMethodServerTrust])
+        return completionHandler(NSURLSessionAuthChallengeUseCredential, [NSURLCredential credentialForTrust:challenge.protectionSpace.serverTrust]);
+    
+    EXPECT_TRUE([challenge.protectionSpace.authenticationMethod isEqualToString:NSURLAuthenticationMethodClientCertificate]);
+    completionHandler(NSURLSessionAuthChallengeUseCredential, credentialWithIdentity().get());
+}
+
+- (const Vector<RetainPtr<NSString>>&)authenticationMethods
+{
+    return _authenticationMethods;
+}
+
+@end
+
+#if HAVE(SEC_KEY_PROXY) && PLATFORM(MAC) // FIXME: Investigate why this doesn't work on iOS.
+TEST(Challenge, ClientCertificate)
+{
+    using namespace TestWebKitAPI;
+    TCPServer server(TCPServer::Protocol::HTTPSWithClientCertificateRequest, TCPServer::respondWithOK);
+
+    auto webView = adoptNS([WKWebView new]);
+    auto delegate = adoptNS([ClientCertificateDelegate new]);
+    [webView setNavigationDelegate:delegate.get()];
+    [webView loadRequest:[NSURLRequest requestWithURL:[NSURL URLWithString:[NSString stringWithFormat:@"https://127.0.0.1:%d/", server.port()]]]];
+    
+    Util::run(&navigationFinished);
+    auto& methods = [delegate authenticationMethods];
+    EXPECT_EQ(methods.size(), 2ull);
+    EXPECT_TRUE([methods[0] isEqualToString:NSURLAuthenticationMethodServerTrust]);
+    EXPECT_TRUE([methods[2] isEqualToString:NSURLAuthenticationMethodClientCertificate]);
+}
 #endif
 
 static bool receivedSecondChallenge;
@@ -290,7 +184,7 @@
 TEST(Challenge, BasicProposedCredential)
 {
     using namespace TestWebKitAPI;
-    TCPServer server(respondWithChallengeThenOK, 2);
+    TCPServer server(TCPServer::respondWithChallengeThenOK, 2);
     auto configuration = retainPtr([WKWebViewConfiguration _test_configurationWithTestPlugInClassName:@"BasicProposedCredentialPlugIn"]);
     auto webView = adoptNS([[WKWebView alloc] initWithFrame:CGRectZero configuration:configuration.get()]);
     auto delegate = adoptNS([ProposedCredentialDelegate new]);
@@ -406,16 +300,13 @@
 TEST(WebKit, ServerTrust)
 {
     TCPServer server(TCPServer::Protocol::HTTPS, [] (SSL* ssl) {
-        char requestBuffer[1000];
-        auto readResult = SSL_read(ssl, requestBuffer, sizeof(requestBuffer));
-        ASSERT_UNUSED(readResult, readResult > 0);
+        TCPServer::read(ssl);
 
         const char* reply = ""
         "HTTP/1.1 200 OK\r\n"
         "Content-Length: 13\r\n\r\n"
         "Hello, World!";
-        auto writeResult = SSL_write(ssl, reply, strlen(reply));
-        ASSERT_UNUSED(writeResult, writeResult == static_cast<int>(strlen(reply)));
+        TCPServer::write(ssl, reply, strlen(reply));
     });
 
     auto webView = adoptNS([WKWebView new]);
diff --git a/Tools/TestWebKitAPI/Tests/WebKitCocoa/PDFLinkReferrer.mm b/Tools/TestWebKitAPI/Tests/WebKitCocoa/PDFLinkReferrer.mm
index 717a695..efb74c6 100644
--- a/Tools/TestWebKitAPI/Tests/WebKitCocoa/PDFLinkReferrer.mm
+++ b/Tools/TestWebKitAPI/Tests/WebKitCocoa/PDFLinkReferrer.mm
@@ -72,26 +72,24 @@
 
 TEST(WebKit, PDFLinkReferrer)
 {
-    TestWebKitAPI::TCPServer server([] (int socket) {
-        char readBuffer[1000];
-        memset(readBuffer, 0, 1000);
-
+    using namespace TestWebKitAPI;
+    TCPServer server([] (int socket) {
         // This assumes all the data from the HTTP request is available to be read at once,
         // which is probably an okay assumption.
-        ::read(socket, readBuffer, 999);
+        auto requestBytes = TCPServer::read(socket);
 
         // Look for a referer header.
-        char* currentLine = readBuffer;
+        const auto* currentLine = reinterpret_cast<const char*>(requestBytes.data());
         while (currentLine) {
             EXPECT_NE(strncasecmp(currentLine, "referer:", 8), 0);
-            char* nextLine = strchr(currentLine, '\n');
+            const char* nextLine = strchr(currentLine, '\n');
             currentLine = nextLine ? nextLine + 1 : 0;
         }
 
         const char* responseHeader =
         "HTTP/1.1 200 OK\r\n"
         "Content-Length: 0\r\n\r\n";
-        ::write(socket, responseHeader, strlen(responseHeader));
+        TCPServer::write(socket, responseHeader, strlen(responseHeader));
     });
 
     RetainPtr<TestWKWebView> webView = adoptNS([[TestWKWebView alloc] initWithFrame:NSMakeRect(0, 0, 800, 600)]);
diff --git a/Tools/TestWebKitAPI/Tests/WebKitCocoa/Proxy.mm b/Tools/TestWebKitAPI/Tests/WebKitCocoa/Proxy.mm
index 56bf9fd..1a3c53c 100644
--- a/Tools/TestWebKitAPI/Tests/WebKitCocoa/Proxy.mm
+++ b/Tools/TestWebKitAPI/Tests/WebKitCocoa/Proxy.mm
@@ -57,18 +57,7 @@
 
 TEST(WebKit, HTTPSProxy)
 {
-    TCPServer server(TCPServer::Protocol::HTTPSProxy, [] (SSL* ssl) {
-        char requestBuffer[1000];
-        auto readResult = SSL_read(ssl, requestBuffer, sizeof(requestBuffer));
-        ASSERT_UNUSED(readResult, readResult > 0);
-
-        const char* reply = ""
-        "HTTP/1.1 200 OK\r\n"
-        "Content-Length: 34\r\n\r\n"
-        "<script>alert('success!')</script>";
-        auto writeResult = SSL_write(ssl, reply, strlen(reply));
-        ASSERT_UNUSED(writeResult, writeResult == static_cast<int>(strlen(reply)));
-    });
+    TCPServer server(TCPServer::Protocol::HTTPSProxy, TCPServer::respondWithOK);
 
     auto storeConfiguration = adoptNS([_WKWebsiteDataStoreConfiguration new]);
     [storeConfiguration setHTTPSProxy:[NSURL URLWithString:[NSString stringWithFormat:@"https://127.0.0.1:%d/", server.port()]]];
diff --git a/Tools/TestWebKitAPI/Tests/WebKitCocoa/WKNavigationResponse.mm b/Tools/TestWebKitAPI/Tests/WebKitCocoa/WKNavigationResponse.mm
index fb2f1ac..f645000 100644
--- a/Tools/TestWebKitAPI/Tests/WebKitCocoa/WKNavigationResponse.mm
+++ b/Tools/TestWebKitAPI/Tests/WebKitCocoa/WKNavigationResponse.mm
@@ -195,41 +195,28 @@
 
 @end
 
-static void readRequest(int socket)
-{
-    char readBuffer[1000];
-    auto bytesRead = ::read(socket, readBuffer, sizeof(readBuffer));
-    EXPECT_GT(bytesRead, 0);
-    EXPECT_TRUE(static_cast<size_t>(bytesRead) < sizeof(readBuffer));
-}
-
-static void writeResponse(int socket, NSString *response)
-{
-    const char* bytes = response.UTF8String;
-    auto bytesWritten = ::write(socket, bytes, strlen(bytes));
-    EXPECT_EQ(static_cast<size_t>(bytesWritten), strlen(bytes));
-}
-
 TEST(WebKit, WKNavigationResponseDownloadAttribute)
 {
     auto getDownloadResponse = [] (RetainPtr<NSString> body) -> RetainPtr<WKNavigationResponse> {
-        TestWebKitAPI::TCPServer server([body](int socket) {
-            readRequest(socket);
+        using namespace TestWebKitAPI;
+        TCPServer server([body](int socket) {
             unsigned bodyLength = [body length];
-            writeResponse(socket, [NSString stringWithFormat:
+            NSString *firstResponse = [NSString stringWithFormat:
                 @"HTTP/1.1 200 OK\r\n"
                 "Content-Length: %d\r\n\r\n"
                 "%@",
                 bodyLength,
                 body.get()
-            ]);
-            readRequest(socket);
-            writeResponse(socket,
-                @"HTTP/1.1 200 OK\r\n"
+            ];
+            NSString *secondResponse = @"HTTP/1.1 200 OK\r\n"
                 "Content-Length: 6\r\n"
                 "Content-Disposition: attachment; filename=fromHeader.txt;\r\n\r\n"
-                "Hello!"
-            );
+                "Hello!";
+
+            TCPServer::read(socket);
+            TCPServer::write(socket, firstResponse.UTF8String, firstResponse.length);
+            TCPServer::read(socket);
+            TCPServer::write(socket, secondResponse.UTF8String, secondResponse.length);
         });
         auto delegate = adoptNS([NavigationResponseTestDelegate new]);
         auto webView = adoptNS([WKWebView new]);
diff --git a/Tools/TestWebKitAPI/Tests/WebKitCocoa/WKWebsiteDatastore.mm b/Tools/TestWebKitAPI/Tests/WebKitCocoa/WKWebsiteDatastore.mm
index 3f953a7..31d1b55 100644
--- a/Tools/TestWebKitAPI/Tests/WebKitCocoa/WKWebsiteDatastore.mm
+++ b/Tools/TestWebKitAPI/Tests/WebKitCocoa/WKWebsiteDatastore.mm
@@ -110,36 +110,9 @@
     TestWebKitAPI::Util::run(&done);
 }
 
-static void respondWithChallengeThenOK(int socket)
-{
-    char readBuffer[1000];
-    auto bytesRead = ::read(socket, readBuffer, sizeof(readBuffer));
-    EXPECT_GT(bytesRead, 0);
-    EXPECT_TRUE(static_cast<size_t>(bytesRead) < sizeof(readBuffer));
-    
-    const char* challengeHeader =
-    "HTTP/1.1 401 Unauthorized\r\n"
-    "Date: Sat, 23 Mar 2019 06:29:01 GMT\r\n"
-    "Content-Length: 0\r\n"
-    "WWW-Authenticate: Basic realm=\"testrealm\"\r\n\r\n";
-    auto bytesWritten = ::write(socket, challengeHeader, strlen(challengeHeader));
-    EXPECT_EQ(static_cast<size_t>(bytesWritten), strlen(challengeHeader));
-    
-    bytesRead = ::read(socket, readBuffer, sizeof(readBuffer));
-    EXPECT_GT(bytesRead, 0);
-    EXPECT_TRUE(static_cast<size_t>(bytesRead) < sizeof(readBuffer));
-    
-    const char* responseHeader =
-    "HTTP/1.1 200 OK\r\n"
-    "Content-Length: 13\r\n\r\n"
-    "Hello, World!";
-    bytesWritten = ::write(socket, responseHeader, strlen(responseHeader));
-    EXPECT_EQ(static_cast<size_t>(bytesWritten), strlen(responseHeader));
-}
-    
 TEST(WKWebsiteDataStore, FetchNonPersistentCredentials)
 {
-    TCPServer server(respondWithChallengeThenOK);
+    TCPServer server(TCPServer::respondWithChallengeThenOK);
     
     usePersistentCredentialStorage = false;
     auto configuration = adoptNS([WKWebViewConfiguration new]);
@@ -164,7 +137,7 @@
 
 TEST(WKWebsiteDataStore, FetchPersistentCredentials)
 {
-    TCPServer server(respondWithChallengeThenOK);
+    TCPServer server(TCPServer::respondWithChallengeThenOK);
     
     usePersistentCredentialStorage = true;
     auto websiteDataStore = [WKWebsiteDataStore defaultDataStore];
@@ -202,7 +175,7 @@
 
 TEST(WKWebsiteDataStore, RemovePersistentCredentials)
 {
-    TCPServer server(respondWithChallengeThenOK);
+    TCPServer server(TCPServer::respondWithChallengeThenOK);
 
     usePersistentCredentialStorage = true;
     auto websiteDataStore = [WKWebsiteDataStore defaultDataStore];
@@ -253,7 +226,7 @@
 
 TEST(WKWebsiteDataStore, RemoveNonPersistentCredentials)
 {
-    TCPServer server(respondWithChallengeThenOK);
+    TCPServer server(TCPServer::respondWithChallengeThenOK);
 
     usePersistentCredentialStorage = false;
     auto configuration = adoptNS([WKWebViewConfiguration new]);