diff --git a/app/service/auth_svc.py b/app/service/auth_svc.py
index 17b2c1aea..b61458657 100644
--- a/app/service/auth_svc.py
+++ b/app/service/auth_svc.py
@@ -62,6 +62,13 @@ def __init__(self):
         self._login_handler = None
         self._default_login_handler = None
 
+    @staticmethod
+    def _ensure_str(value) -> str:
+        """Convert a value to str safely, decoding bytes instead of using str() repr."""
+        if isinstance(value, bytes):
+            return value.decode('utf-8', errors='replace')
+        return str(value)
+
     @property
     def default_login_handler(self):
         return self._default_login_handler
@@ -170,9 +177,12 @@ async def get_permissions(self, request):
         identity = await identity_policy.identify(request)
         if identity in self.user_map:
             return [self.Access[p.upper()] for p in self.user_map[identity].permissions]
-        elif request.headers.get(HEADER_API_KEY) == self.get_config(CONFIG_API_KEY_RED):
+        request_key = self._ensure_str(request.headers.get(HEADER_API_KEY) or '')
+        red_key = self._ensure_str(self.get_config(CONFIG_API_KEY_RED) or '')
+        blue_key = self._ensure_str(self.get_config(CONFIG_API_KEY_BLUE) or '')
+        if red_key and compare_digest(request_key, red_key):
             return self.Access.RED, self.Access.APP
-        elif request.headers.get(HEADER_API_KEY) == self.get_config(CONFIG_API_KEY_BLUE):
+        elif blue_key and compare_digest(request_key, blue_key):
             return self.Access.BLUE, self.Access.APP
         return ()
 
diff --git a/tests/test_compare_digest_auth.py b/tests/test_compare_digest_auth.py
new file mode 100644
index 000000000..4cb50cda4
--- /dev/null
+++ b/tests/test_compare_digest_auth.py
@@ -0,0 +1,85 @@
+import pytest
+from unittest.mock import MagicMock, AsyncMock
+from app.service.auth_svc import AuthService, HEADER_API_KEY
+from app.utility.base_world import BaseWorld
+
+
+@pytest.fixture(autouse=True)
+def setup_config():
+    BaseWorld.apply_config('main', {
+        'api_key_red': 'RED_KEY_123',
+        'api_key_blue': 'BLUE_KEY_456',
+    })
+    yield
+    BaseWorld.clear_config()
+
+
+class MockHeaders:
+    def __init__(self, data):
+        self._data = data
+
+    def get(self, key, default=None):
+        return self._data.get(key, default)
+
+
+class TestCompareDigestAuth:
+    def _make_request(self, api_key=None):
+        request = MagicMock()
+        headers_data = {HEADER_API_KEY: api_key} if api_key else {}
+        request.headers = MockHeaders(headers_data)
+        identity_policy = AsyncMock()
+        identity_policy.identify = AsyncMock(return_value=None)
+        request.config_dict = {'aiohttp_security_identity_policy': identity_policy}
+        return request
+
+    @pytest.mark.asyncio
+    async def test_red_key_returns_red_access(self):
+        svc = AuthService.__new__(AuthService)
+        svc.user_map = {}
+        request = self._make_request('RED_KEY_123')
+        result = await svc.get_permissions(request)
+        assert BaseWorld.Access.RED in result
+        assert BaseWorld.Access.APP in result
+
+    @pytest.mark.asyncio
+    async def test_blue_key_returns_blue_access(self):
+        svc = AuthService.__new__(AuthService)
+        svc.user_map = {}
+        request = self._make_request('BLUE_KEY_456')
+        result = await svc.get_permissions(request)
+        assert BaseWorld.Access.BLUE in result
+        assert BaseWorld.Access.APP in result
+
+    @pytest.mark.asyncio
+    async def test_wrong_key_returns_empty(self):
+        svc = AuthService.__new__(AuthService)
+        svc.user_map = {}
+        request = self._make_request('WRONG_KEY')
+        result = await svc.get_permissions(request)
+        assert result == ()
+
+    @pytest.mark.asyncio
+    async def test_no_key_returns_empty(self):
+        svc = AuthService.__new__(AuthService)
+        svc.user_map = {}
+        request = self._make_request(None)
+        result = await svc.get_permissions(request)
+        assert result == ()
+
+    def test_ensure_str_decodes_bytes(self):
+        """bytes values should be decoded, not repr'd as 'b\"...\"'."""
+        assert AuthService._ensure_str(b'KEY123') == 'KEY123'
+        assert AuthService._ensure_str('KEY123') == 'KEY123'
+
+    @pytest.mark.asyncio
+    async def test_bytes_config_key_matches(self):
+        """If config returns bytes, compare_digest should still match the str header."""
+        BaseWorld.apply_config('main', {
+            'api_key_red': b'RED_KEY_123',
+            'api_key_blue': b'BLUE_KEY_456',
+        })
+        svc = AuthService.__new__(AuthService)
+        svc.user_map = {}
+        request = self._make_request('RED_KEY_123')
+        result = await svc.get_permissions(request)
+        assert BaseWorld.Access.RED in result