Lay foundation for truly dynamic external logins

Moves all the external login services into a set of classes that share as much code as possible. These services are then registered on both the client and server, allowing us in the followup change to dynamically register new handlers

endpoints/common.py

@@ -16,7 +16,7 @@ from flask_principal import identity_changed
 import endpoints.decorated # Register the various exceptions via decorators.
 import features
 
-from app import app, oauth_apps, LoginWrappedDBUser, user_analytics, license_validator
+from app import app, oauth_apps, oauth_login, LoginWrappedDBUser, user_analytics, license_validator
 from auth import scopes
 from auth.permissions import QuayDeferredPermissionUser
 from config import frontend_visible_config
@@ -189,6 +189,19 @@ def render_page_template(name, route_data=None, **kwargs):
       cache_buster = cachebusters.get(filename, random_string()) if not debugging else 'debugging'
       yield (filename, cache_buster)
 
+  def get_external_login_config():
+    login_config = []
+    for login_service in oauth_login.services:
+      login_config.append({
+        'id': login_service.service_id(),
+        'title': login_service.service_name(),
+        'config': login_service.get_public_config(),
+        'icon': login_service.get_icon(),
+        'scopes': login_service.get_login_scopes(),
+      })
+
+    return login_config
+
   def get_oauth_config():
     oauth_config = {}
     for oauth_app in oauth_apps:
@@ -215,6 +228,7 @@ def render_page_template(name, route_data=None, **kwargs):
                                        feature_set=features.get_features(),
                                        config_set=frontend_visible_config(app.config),
                                        oauth_set=get_oauth_config(),
+                                       external_login_set=get_external_login_config(),
                                        scope_set=scopes.app_scopes(app.config),
                                        vuln_priority_set=PRIORITY_LEVELS,
                                        enterprise_logo=app.config.get('ENTERPRISE_LOGO_URL', ''),