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

components/proximity_auth/cryptauth/cryptauth_enrollment_utils.h

Index: components/proximity_auth/cryptauth/cryptauth_enrollment_utils.h
diff --git a/components/proximity_auth/cryptauth/cryptauth_enrollment_utils.h b/components/proximity_auth/cryptauth/cryptauth_enrollment_utils.h
index 0bebd1a2b1123dc25cef21e7a5571627267b8795..77a07854230b414f23f27dde624be0171967d993 100644
--- a/components/proximity_auth/cryptauth/cryptauth_enrollment_utils.h
+++ b/components/proximity_auth/cryptauth/cryptauth_enrollment_utils.h
@@ -7,11 +7,15 @@
 
 #include <string>
 
+namespace user_manager {
+class UserID;
+}
+
 namespace proximity_auth {
 
 // Calculates an id for the specified user on the specified device.
 std::string CalculateDeviceUserId(const std::string& device_id,
-                                  const std::string& user_id);
+                                  const user_manager::UserID& user_id);
 
 }  // namespace proximity_auth