diff --git a/.secrets.baseline b/.secrets.baseline
index 83a918e..8fa770f 100644
--- a/.secrets.baseline
+++ b/.secrets.baseline
@@ -289,7 +289,7 @@
         "filename": "src/api/hive_auth_async.py",
         "hashed_secret": "576956b5291ac38d04ef5f82cc974286a857f0b2",
         "is_verified": false,
-        "line_number": 113
+        "line_number": 128
       }
     ],
     "src/api/srp_crypto.py": [
@@ -580,5 +580,5 @@
       }
     ]
   },
-  "generated_at": "2026-09-26T17:01:30Z"
+  "generated_at": "2026-10-20T19:58:38Z"
 }
diff --git a/src/api/hive_auth.py b/src/api/hive_auth.py
index 793e3d8..50d37d6 100644
--- a/src/api/hive_auth.py
+++ b/src/api/hive_auth.py
@@ -126,6 +126,21 @@ def __init__(  # pylint: disable=too-many-positional-arguments  # noqa: PLR0913
             aws_session_token="SESSION_TOKEN",
         )
 
+    @property
+    def username(self) -> str:
+        """Return the Hive username, normalised for Cognito."""
+        return self._username
+
+    @username.setter
+    def username(self, value: str) -> None:
+        """Store the username trimmed and lower-cased.
+
+        Hive's Cognito pool treats the email as case-sensitive, so a
+        capitalised address (e.g. from mobile autocapitalisation) fails
+        with an invalid-password error even though the account exists.
+        """
+        self._username = value.strip().lower() if isinstance(value, str) else value
+
     def generate_random_small_a(self):
         """Helper function to generate a random big integer.
 
diff --git a/src/api/hive_auth_async.py b/src/api/hive_auth_async.py
index 378e7a9..66a215d 100644
--- a/src/api/hive_auth_async.py
+++ b/src/api/hive_auth_async.py
@@ -88,6 +88,21 @@ def __init__(  # pylint: disable=too-many-positional-arguments  # noqa: PLR0913
         self._region: str | None = None
         self.client: Any = None
 
+    @property
+    def username(self) -> str:
+        """Return the Hive username, normalised for Cognito."""
+        return self._username
+
+    @username.setter
+    def username(self, value: str) -> None:
+        """Store the username trimmed and lower-cased.
+
+        Hive's Cognito pool treats the email as case-sensitive, so a
+        capitalised address (e.g. from mobile autocapitalisation) fails
+        with an invalid-password error even though the account exists.
+        """
+        self._username = value.strip().lower() if isinstance(value, str) else value
+
     async def async_init(self):
         """Initialise async variables."""
         self.loop = asyncio.get_running_loop()
diff --git a/tests/unit/test_hive_auth.py b/tests/unit/test_hive_auth.py
index 746b9c0..ebc1522 100644
--- a/tests/unit/test_hive_auth.py
+++ b/tests/unit/test_hive_auth.py
@@ -1279,3 +1279,16 @@ def test_without_client_secret_no_secret_hash(self):
             response = auth.process_device_challenge(params)
 
         assert "SECRET_HASH" not in response
+
+
+class TestUsernameNormalisation:
+    """Hive's Cognito pool is case-sensitive; usernames are lower-cased."""
+
+    def test_constructor_normalises_username(self):
+        auth = _make_auth(username="  User@Example.COM ")
+        assert auth.username == "user@example.com"
+
+    def test_reassignment_is_normalised(self):
+        auth = _make_auth()
+        auth.username = "Someone@Example.com"
+        assert auth.username == "someone@example.com"
diff --git a/tests/unit/test_hive_auth_async.py b/tests/unit/test_hive_auth_async.py
index 5a0114b..6caab7f 100644
--- a/tests/unit/test_hive_auth_async.py
+++ b/tests/unit/test_hive_auth_async.py
@@ -1428,3 +1428,30 @@ async def test_async_init_raises_when_login_info_is_none(self):
         with patch("asyncio.get_running_loop", return_value=mock_loop):
             with pytest.raises(HiveUnknownConfiguration):
                 await auth.async_init()
+
+
+class TestUsernameNormalisation:
+    """Hive's Cognito pool is case-sensitive; usernames are lower-cased."""
+
+    @pytest.mark.parametrize(
+        "typed",
+        ["User@Example.com", "USER@EXAMPLE.COM", "  user@example.com  "],
+    )
+    async def test_constructor_normalises_username(self, typed):
+        auth = await _make_auth(username=typed)
+        assert auth.username == "user@example.com"
+
+    async def test_reassignment_is_normalised(self):
+        """start_session reassigns auth.username from the HA config entry."""
+        auth = await _make_auth()
+        auth.username = "Someone@Example.com"
+        assert auth.username == "someone@example.com"
+
+    async def test_initiate_auth_sends_lowercase_username(self):
+        auth = await _make_auth(username="User@Example.com")
+        params = await auth.get_auth_params()
+        assert params["USERNAME"] == "user@example.com"
+
+    async def test_file_mode_detected_with_any_case(self):
+        auth = await _make_auth(username="Use@File.com")
+        assert auth.use_file is True