[verified] fix(auth): support Unicode credentials

tests/test_dashboard_authentication.py

@@ -63,20 +63,26 @@ def test_load_admin_credentials_fails_closed_when_environment_cannot_be_read():
 
 def test_verify_credentials_uses_constant_time_comparison_for_both_fields(monkeypatch):
     credentials = authentication.AdminCredentials(ADMIN_ID, ADMIN_PASSWORD)
-    comparisons: list[tuple[str, str]] = []
+    comparisons: list[tuple[bytes, bytes]] = []
 
-    def record_compare(left: str, right: str) -> bool:
+    def record_compare(left: bytes, right: bytes) -> bool:
         comparisons.append((left, right))
         return left == right
 
     monkeypatch.setattr(authentication.hmac, "compare_digest", record_compare)
 
     assert authentication.verify_credentials(credentials, ADMIN_ID, ADMIN_PASSWORD) is True
-    assert comparisons == [(ADMIN_ID, ADMIN_ID), (ADMIN_PASSWORD, ADMIN_PASSWORD)]
+    assert comparisons == [
+        (ADMIN_ID.encode("utf-8"), ADMIN_ID.encode("utf-8")),
+        (ADMIN_PASSWORD.encode("utf-8"), ADMIN_PASSWORD.encode("utf-8")),
+    ]
 
     comparisons.clear()
     assert authentication.verify_credentials(credentials, "wrong-id", "wrong-password") is False
-    assert comparisons == [("wrong-id", ADMIN_ID), ("wrong-password", ADMIN_PASSWORD)]
+    assert comparisons == [
+        (b"wrong-id", ADMIN_ID.encode("utf-8")),
+        (b"wrong-password", ADMIN_PASSWORD.encode("utf-8")),
+    ]
 
 
 def test_failed_login_delay_waits_only_for_remaining_minimum_duration():