diff --git a/fastapi_opa/auth/auth_saml.py b/fastapi_opa/auth/auth_saml.py
index 61d3815..dc7a07d 100644
--- a/fastapi_opa/auth/auth_saml.py
+++ b/fastapi_opa/auth/auth_saml.py
@@ -44,7 +44,7 @@ async def authenticate(
         elif 'sso2' in request.query_params:
             logger.debug(datetime.utcnow(), '--sso2--')
             return_to = '%sattrs/' % request.base_url
-            return RedirectResponse(auth.login(return_to))
+            return await self.single_sign_on(auth, return_to)
         elif "acs" in request.query_params:
             logger.debug(datetime.utcnow(), '--acs--')
             return await self.assertion_consumer_service(auth, request_args, request)
@@ -93,8 +93,8 @@ async def single_log_out(auth: OneLogin_Saml2_Auth) -> RedirectResponse:
                         spnq=name_id_spnq))
 
     @staticmethod
-    async def single_sign_on(auth: OneLogin_Saml2_Auth) -> RedirectResponse:
-        redirect_url = auth.login()
+    async def single_sign_on(auth: OneLogin_Saml2_Auth, url: str = None) -> RedirectResponse:
+        redirect_url = auth.login(url)
         return RedirectResponse(redirect_url)
 
     @staticmethod
diff --git a/tests/test_saml_auth.py b/tests/test_saml_auth.py
index 3bae4e9..0ae92a7 100644
--- a/tests/test_saml_auth.py
+++ b/tests/test_saml_auth.py
@@ -15,12 +15,30 @@ async def test_single_sign_on():
 
     saml_auth_mock = Mock()
     saml_auth_mock.login.return_value = "http://idp.com/cryptic-stuff"
-    response = await saml_auth.single_sign_on(saml_auth_mock)
+    url = r"http://idp.com/cryptic-stuff/attrs"
+    response = await saml_auth.single_sign_on(saml_auth_mock, url)
 
     assert isinstance(response, RedirectResponse)
     assert response.headers.get("location") == "http://idp.com/cryptic-stuff"
 
 
+@pytest.mark.asyncio
+async def test_single_sign_on_with_parameter():
+    saml_conf = SAMLConfig(settings_directory="./tests/test_data/saml")
+    saml_auth = SAMLAuthentication(saml_conf)
+
+    def side_effect(url):
+        return url
+
+    saml_auth_mock = Mock()
+    saml_auth_mock.login = Mock(side_effect=side_effect)
+    attr_url = "http://idp.com/cryptic-stuff/attrs"
+    response = await saml_auth.single_sign_on(saml_auth_mock, attr_url)
+
+    assert isinstance(response, RedirectResponse)
+    assert response.headers.get("location") == attr_url
+
+
 @pytest.mark.asyncio
 @patch("fastapi_opa.auth.auth_saml.OneLogin_Saml2_Utils")
 async def test_assertion_consumer_service(saml_util_mock):