diff --git a/oauth/oidc.py b/oauth/oidc.py
index e19e5c466..232ef68ae 100644
--- a/oauth/oidc.py
+++ b/oauth/oidc.py
@@ -2,6 +2,7 @@ import time
 import json
 import logging
 import urlparse
+import urllib
 
 import jwt
 
@@ -65,13 +66,35 @@ class OIDCLoginService(OAuthService):
     return list(set(login_scopes) & set(supported_scopes))
 
   def authorize_endpoint(self):
-    return self._oidc_config().get('authorization_endpoint', '') + '?response_type=code&'
+    return self._get_endpoint('authorization_endpoint', response_type='code')
 
   def token_endpoint(self):
-    return self._oidc_config().get('token_endpoint')
+    return self._get_endpoint('token_endpoint')
 
   def user_endpoint(self):
-    return self._oidc_config().get('userinfo_endpoint')
+    return self._get_endpoint('userinfo_endpoint')
+
+  def _get_endpoint(self, endpoint_key, **kwargs):
+    """ Returns the OIDC endpoint with the given key found in the OIDC discovery
+        document, with the given kwargs added as query parameters. Additionally,
+        any defined parameters found in the OIDC configuration block are also
+        added.
+    """
+    endpoint = self._oidc_config().get(endpoint_key, '')
+    if not endpoint:
+      return None
+
+    (scheme, netloc, path, query, fragment) = urlparse.urlsplit(endpoint)
+
+    # Add the query parameters from the kwargs and the config.
+    custom_parameters = self.config.get('OIDC_ENDPOINT_CUSTOM_PARAMS', {}).get(endpoint_key, {})
+
+    query_params = urlparse.parse_qs(query, keep_blank_values=True)
+    query_params.update(kwargs)
+    query_params.update(custom_parameters)
+
+    updated_query = urllib.urlencode(query_params)
+    return urlparse.urlunsplit((scheme, netloc, path, updated_query, fragment))
 
   def validate(self):
     return bool(self.get_login_scopes())
diff --git a/oauth/test/test_oidc.py b/oauth/test/test_oidc.py
index 73208cbe4..aaa7d9774 100644
--- a/oauth/test/test_oidc.py
+++ b/oauth/test/test_oidc.py
@@ -79,6 +79,20 @@ def app_config(http_client, mailing_feature):
       'DEBUGGING': True,
     },
 
+    'OIDCWITHPARAMS_LOGIN_CONFIG': {
+      'CLIENT_ID': 'foo',
+      'CLIENT_SECRET': 'bar',
+      'SERVICE_NAME': 'Some Other Service',
+      'SERVICE_ICON': 'http://some/icon',
+      'OIDC_SERVER': 'http://fakeoidc',
+      'DEBUGGING': True,
+      'OIDC_ENDPOINT_CUSTOM_PARAMS': {
+        'authorization_endpoint': {
+          'some': 'param',
+        },
+      },
+    },
+
     'HTTPCLIENT': http_client,
   }
 
@@ -90,6 +104,10 @@ def oidc_service(app_config):
 def another_oidc_service(app_config):
   return OIDCLoginService(app_config, 'ANOTHEROIDC_LOGIN_CONFIG')
 
+@pytest.fixture()
+def oidc_withparams_service(app_config):
+  return OIDCLoginService(app_config, 'OIDCWITHPARAMS_LOGIN_CONFIG')
+
 @pytest.fixture()
 def discovery_content(userinfo_supported):
   return {
@@ -218,13 +236,18 @@ def test_basic_config(oidc_service):
 
 def test_discovery(oidc_service, http_client, discovery_content, discovery_handler):
   with HTTMock(discovery_handler):
-    auth = discovery_content['authorization_endpoint'] + '?response_type=code&'
+    auth = discovery_content['authorization_endpoint'] + '?response_type=code'
     assert oidc_service.authorize_endpoint() == auth
 
     assert oidc_service.token_endpoint() == discovery_content['token_endpoint']
     assert oidc_service.user_endpoint() == discovery_content['userinfo_endpoint']
     assert set(oidc_service.get_login_scopes()) == set(discovery_content['scopes_supported'])
 
+def test_discovery_with_params(oidc_withparams_service, http_client, discovery_content, discovery_handler):
+  with HTTMock(discovery_handler):
+    auth = discovery_content['authorization_endpoint'] + '?response_type=code&some=param'
+    assert 'some=param' in oidc_withparams_service.authorize_endpoint()
+
 def test_filtered_discovery(another_oidc_service, http_client, discovery_content, discovery_handler):
   with HTTMock(discovery_handler):
     assert another_oidc_service.get_login_scopes() == ['openid']