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/directives/ui/signup-form.js

@@ -13,11 +13,13 @@ angular.module('quay').directive('signupForm', function () {
       'hideRegisteredMessage': '@hideRegisteredMessage',
       'userRegistered': '&userRegistered'
     },
-    controller: function($scope, $location, $timeout, ApiService, KeyService, UserService, Config, UIService) {
+    controller: function($scope, $location, $timeout, ApiService, KeyService, UserService, Config, UIService, ExternalLoginService) {
       $('.form-signup').popover();
 
       $scope.awaitingConfirmation = false;
       $scope.registering = false;
+      $scope.EXTERNAL_LOGINS = ExternalLoginService.EXTERNAL_LOGINS;
+      $scope.singleSigninUrl = ExternalLoginService.getSingleSigninUrl();
 
       $scope.register = function() {
         UIService.hidePopover('#signupButton');