We should use UserID object to identify users instead of username.

chrome/browser/extensions/api/enterprise_platform_keys_private/enterprise_platform_keys_private_api.h

Index: chrome/browser/extensions/api/enterprise_platform_keys_private/enterprise_platform_keys_private_api.h
diff --git a/chrome/browser/extensions/api/enterprise_platform_keys_private/enterprise_platform_keys_private_api.h b/chrome/browser/extensions/api/enterprise_platform_keys_private/enterprise_platform_keys_private_api.h
index 49f334f69f8300e2c114aab2e21c526754ae4037..31f78c8cafbd5a13e20548d8b62d527a6c7f8d8d 100644
--- a/chrome/browser/extensions/api/enterprise_platform_keys_private/enterprise_platform_keys_private_api.h
+++ b/chrome/browser/extensions/api/enterprise_platform_keys_private/enterprise_platform_keys_private_api.h
@@ -16,6 +16,7 @@
 #include "chromeos/attestation/attestation_flow.h"
 #include "chromeos/dbus/cryptohome_client.h"
 #include "chromeos/dbus/dbus_method_call_status.h"
+#include "components/user_manager/user_id.h"
 #include "third_party/cros_system_api/dbus/service_constants.h"
 
 class PrefService;
@@ -81,8 +82,8 @@ class EPKPChallengeKeyBase : public ChromeAsyncExtensionFunction {
   // Returns the enterprise domain the device is enrolled to.
   std::string GetEnterpriseDomain() const;
 
-  // Returns the user email.
-  std::string GetUserEmail() const;
+  // Returns the user ID.
+  user_manager::UserID GetUserID() const;
 
   // Returns the enterprise virtual device ID.
   std::string GetDeviceId() const;
@@ -93,7 +94,7 @@ class EPKPChallengeKeyBase : public ChromeAsyncExtensionFunction {
   // user consent before calling GetCertificate().
   void PrepareKey(
       chromeos::attestation::AttestationKeyType key_type,
-      const std::string& user_id,
+      const user_manager::UserID& user_id,
       const std::string& key_name,
       chromeos::attestation::AttestationCertificateProfile certificate_profile,
       bool require_user_consent,
@@ -109,7 +110,7 @@ class EPKPChallengeKeyBase : public ChromeAsyncExtensionFunction {
   struct PrepareKeyContext {
     PrepareKeyContext(
         chromeos::attestation::AttestationKeyType key_type,
-        const std::string& user_id,
+        const user_manager::UserID& user_id,
         const std::string& key_name,
         chromeos::attestation::AttestationCertificateProfile
             certificate_profile,
@@ -118,7 +119,7 @@ class EPKPChallengeKeyBase : public ChromeAsyncExtensionFunction {
     ~PrepareKeyContext();
 
     chromeos::attestation::AttestationKeyType key_type;
-    const std::string user_id;
+    const user_manager::UserID user_id;
     const std::string key_name;
     chromeos::attestation::AttestationCertificateProfile certificate_profile;
     bool require_user_consent;