diff --git a/src/flask_pyoidc/flask_pyoidc.py b/src/flask_pyoidc/flask_pyoidc.py
index 5ca699f..cd00461 100644
--- a/src/flask_pyoidc/flask_pyoidc.py
+++ b/src/flask_pyoidc/flask_pyoidc.py
@@ -183,7 +183,7 @@ class OIDCAuthentication:
             # if the current request was from the JS page handling fragment encoded responses we need to return
             # a URL for the error page to redirect to
             flask.session['error'] = error_response
-            return '/' + self._redirect_uri_endpoint + '?error=1'
+            return '/' + self._redirect_uri_config.endpoint + '?error=1'
         return self._show_error_response(error_response)
 
     def _show_error_response(self, error_response):

diff --git a/tests/test_flask_pyoidc.py b/tests/test_flask_pyoidc.py
index 427cdf9..e507adc 100644
--- a/tests/test_flask_pyoidc.py
+++ b/tests/test_flask_pyoidc.py
@@ -290,6 +290,24 @@ class TestOIDCAuthentication(object):
             assert session.access_token == access_token
             assert response == '/test'
 
+    def test_handle_error_response_POST(self):
+        state = 'test_state'
+
+        authn = self.init_app()
+        error_resp = {'state': state, 'error': 'invalid_request', 'error_description': 'test error'}
+
+        with self.app.test_request_context('/redirect_uri',
+                                           method='POST',
+                                           data=error_resp,
+                                           mimetype='application/x-www-form-urlencoded'):
+            UserSession(flask.session, self.PROVIDER_NAME)
+            flask.session['state'] = state
+            flask.session['nonce'] = 'test_nonce'
+            response = authn._handle_authentication_response()
+            assert flask.session['error'] == error_resp
+            assert response == '/redirect_uri?error=1'
+
+
     def test_handle_authentication_response_without_initialised_session(self):
         authn = self.init_app()
 

Error responses using undefined _redirect_uri_endpoint attribute

In some cases (e.g. when the auth state goes stale after much time) we rightfully receive an error that should be passed on to the client

```python
Exception on /redirect_uri [POST]

Traceback (most recent call last):

  File "../flask_pyoidc/flask_pyoidc.py", line 156, in _handle_authentication_response

    flask.session.pop('nonce'))

  File "../lib/python3.7/site-packages/flask_pyoidc/auth_response_handler.py", line 60, in process_auth_response

    raise AuthResponseErrorResponseError(auth_response.to_dict())

flask_pyoidc.auth_response_handler.AuthResponseErrorResponseError: {'error': 'login_required', 'state': 'm92iSPHP7qMBXSkQ'}

 

During handling of the above exception, another exception occurred:

 

Traceback (most recent call last):

  File "../lib/python3.7/site-packages/flask/app.py", line 2447, in wsgi_app

    response = self.full_dispatch_request()

  File "../lib/python3.7/site-packages/flask/app.py", line 1952, in full_dispatch_request

    rv = self.handle_user_exception(e)

  File "../lib/python3.7/site-packages/flask_cors/extension.py", line 165, in wrapped_function

    return cors_after_request(app.make_response(f(*args, **kwargs)))

  File "../lib/python3.7/site-packages/flask_cors/extension.py", line 165, in wrapped_function

    return cors_after_request(app.make_response(f(*args, **kwargs)))

  File "../lib/python3.7/site-packages/flask/app.py", line 1821, in handle_user_exception

    reraise(exc_type, exc_value, tb)

  File "../lib/python3.7/site-packages/flask/_compat.py", line 39, in reraise

    raise value

  File "../lib/python3.7/site-packages/flask/app.py", line 1950, in full_dispatch_request

    rv = self.dispatch_request()

  File "../lib/python3.7/site-packages/flask/app.py", line 1936, in dispatch_request

    return self.view_functions[rule.endpoint](**req.view_args)

  File "../lib/python3.7/site-packages/flask_pyoidc/flask_pyoidc.py", line 158, in _handle_authentication_response

    return self._handle_error_response(e.error_response, is_processing_fragment_encoded_response)

  File "../lib/python3.7/site-packages/flask_pyoidc/flask_pyoidc.py", line 186, in _handle_error_response

    return '/' + self._redirect_uri_endpoint + '?error=1'

AttributeError: 'OIDCAuthentication' object has no attribute '_redirect_uri_endpoint'
```

Unfortunately it looks like the error handler tries to return a nonexistant attribute (holdover from old code?) for the redirect uri endpoint. I'm guessing this should be 
`self._redirect_uri_config.endpoint` instead.
tests/test_flask_pyoidc.py::TestOIDCAuthentication::test_handle_error_response_POST
tests/test_flask_pyoidc.py::TestOIDCAuthentication::test_should_register_client_if_not_registered_before[None] tests/test_flask_pyoidc.py::TestOIDCAuthentication::test_handle_authentication_response_fragment_encoded tests/test_flask_pyoidc.py::TestOIDCAuthentication::test_logout_redirects_to_provider_if_end_session_endpoint_is_configured[https://example.com/post_logout] tests/test_flask_pyoidc.py::TestOIDCAuthentication::test_handle_authentication_response_without_stored_nonce tests/test_flask_pyoidc.py::TestOIDCAuthentication::test_logout_handles_no_user_session tests/test_flask_pyoidc.py::TestOIDCAuthentication::test_reauthenticate_silent_if_session_expired tests/test_flask_pyoidc.py::TestOIDCAuthentication::test_should_not_refresh_still_valid_access_token tests/test_flask_pyoidc.py::TestOIDCAuthentication::test_logout_handles_redirect_back_from_provider_with_incorrect_state tests/test_flask_pyoidc.py::TestOIDCAuthentication::test_handle_authentication_response_POST tests/test_flask_pyoidc.py::TestOIDCAuthentication::test_handle_authentication_response_without_initialised_session tests/test_flask_pyoidc.py::TestOIDCAuthentication::test_handle_authentication_response tests/test_flask_pyoidc.py::TestOIDCAuthentication::test_expected_auth_response_mode_is_set[code-False] tests/test_flask_pyoidc.py::TestOIDCAuthentication::test_should_not_refresh_access_token_without_expiry tests/test_flask_pyoidc.py::TestOIDCAuthentication::test_should_not_refresh_without_refresh_token tests/test_flask_pyoidc.py::TestOIDCAuthentication::test_handle_authentication_response_without_stored_state tests/test_flask_pyoidc.py::TestOIDCAuthentication::test_should_not_refresh_if_no_user_session tests/test_flask_pyoidc.py::TestOIDCAuthentication::test_token_error_response_returns_default_error_if_no_error_view_set tests/test_flask_pyoidc.py::TestOIDCAuthentication::test_token_error_response_calls_to_error_view_if_set tests/test_flask_pyoidc.py::TestOIDCAuthentication::test_should_register_client_if_not_registered_before[post_logout_redirect_uris1] tests/test_flask_pyoidc.py::TestOIDCAuthentication::test_expected_auth_response_mode_is_set[id_token tests/test_flask_pyoidc.py::TestOIDCAuthentication::test_logout_handles_provider_without_end_session_endpoint tests/test_flask_pyoidc.py::TestOIDCAuthentication::test_logout_redirects_to_provider_if_end_session_endpoint_is_configured[None] tests/test_flask_pyoidc.py::TestOIDCAuthentication::test_authentication_error_response_returns_default_error_if_no_error_view_set tests/test_flask_pyoidc.py::TestOIDCAuthentication::test_using_unknown_provider_name_should_raise_exception tests/test_flask_pyoidc.py::TestOIDCAuthentication::test_dont_reauthenticate_silent_if_session_not_expired tests/test_flask_pyoidc.py::TestOIDCAuthentication::test_should_return_None_if_token_refresh_request_fails tests/test_flask_pyoidc.py::TestOIDCAuthentication::test_handle_authentication_response_error_message tests/test_flask_pyoidc.py::TestOIDCAuthentication::test_should_refresh_expired_access_token tests/test_flask_pyoidc.py::TestOIDCAuthentication::test_should_authenticate_if_no_session tests/test_flask_pyoidc.py::TestOIDCAuthentication::test_handle_implicit_authentication_response tests/test_flask_pyoidc.py::TestOIDCAuthentication::test_should_not_authenticate_if_session_exists tests/test_flask_pyoidc.py::TestOIDCAuthentication::test_handle_authentication_response_error_message_without_stored_error tests/test_flask_pyoidc.py::TestOIDCAuthentication::test_should_refresh_still_valid_access_token_if_forced tests/test_flask_pyoidc.py::TestOIDCAuthentication::test_logout_handles_redirect_back_from_provider tests/test_flask_pyoidc.py::TestOIDCAuthentication::test_authentication_error_response_calls_to_error_view_if_set