[Secure Payment Confirmation] Random user identifier.

Before this patch, creating two payment credentials in Touch ID with
identical instrument display name and relying party would erase the
first credential, so it could no longer be exercised.

This patch uses a random 32 byte array instead of instrument display
name as the user identifier.

After this patch, a relying party can create a large number of payment
credentials with identical instrument display name, so all of them can
still be exercised.

Bug: 1139040
Change-Id: I68895c4b7d6bb64afa1f44e2b30a613ab6293023
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2487220Reviewed-by: Ken Buchanan <kenrb@chromium.org>
Commit-Queue: Rouslan Solomakhin <rouslan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#819053}

third_party/blink/renderer/modules/credentialmanager/credentials_container.cc

@@ -8,6 +8,7 @@
 #include <utility>
 
 #include "base/metrics/histogram_macros.h"
+#include "base/rand_util.h"
 #include "build/build_config.h"
 #include "third_party/blink/public/common/sms/webotp_service_outcome.h"
 #include "third_party/blink/public/mojom/credentialmanager/credential_manager.mojom-blink.h"
@@ -61,6 +62,7 @@
 #include "third_party/blink/renderer/platform/weborigin/origin_access_entry.h"
 #include "third_party/blink/renderer/platform/weborigin/security_origin.h"
 #include "third_party/blink/renderer/platform/wtf/functional.h"
+#include "third_party/blink/renderer/platform/wtf/wtf_size_t.h"
 
 #if defined(OS_ANDROID)
 #include "third_party/blink/renderer/bindings/modules/v8/v8_public_key_credential_rp_entity.h"
@@ -750,15 +752,10 @@ void CreatePublicKeyCredentialForPaymentCredential(
   mojo_options->user = mojom::blink::PublicKeyCredentialUserEntity::New();
   mojo_options->user->name = options->instrument()->displayName();
 
-  // There isn't explicity a WebAuthn 'user ID', so just convert the
-  // instrument display name into a byte array and use that.
-  const uint8_t* display_name_bytes =
-      static_cast<const uint8_t*>(options->instrument()->displayName().Bytes());
-  mojo_options->user->id = Vector<uint8_t>();
-  mojo_options->user->id.AppendRange(
-      display_name_bytes,
-      display_name_bytes +
-          options->instrument()->displayName().CharactersSizeInBytes());
+  static constexpr wtf_size_t kRandomUserIdSize = 32;
+  mojo_options->user->id = Vector<uint8_t>(kRandomUserIdSize);
+  base::RandBytes(mojo_options->user->id.data(), kRandomUserIdSize);
+
   mojo_options->user->display_name = options->instrument()->displayName();
   mojo_options->user->icon = KURL(options->instrument()->icon());