Add support for Dex to Quay

Fixes #306

- Adds support for Dex as an OAuth external login provider
- Adds support for OIDC in general
- Extract out external logins on the JS side into a service
- Add a feature flag for disabling direct login
- Add support for directing to the single external login service
- Does *not* yet support the config in the superuser tool

static/js/pages/user-view.js

@@ -10,7 +10,7 @@
     })
   }]);
 
-  function UserViewCtrl($scope, $routeParams, $timeout, ApiService, UserService, UIService, AvatarService, Config) {
+  function UserViewCtrl($scope, $routeParams, $timeout, ApiService, UserService, UIService, AvatarService, Config, ExternalLoginService) {
     var username = $routeParams.username;
 
     $scope.showInvoicesCounter = 0;
@@ -18,6 +18,7 @@
     $scope.showRobotsCounter = 0;
     $scope.changeEmailInfo = {};
     $scope.changePasswordInfo = {};
+    $scope.hasSingleSignin = ExternalLoginService.hasSingleSignin();
 
     UserService.updateUserIn($scope);