Add new afterLogin cloud code hook (#6387)

* add new afterLogin cloud code hook

* include user on req.user for afterLogin hook

src/triggers.js

@@ -4,6 +4,7 @@ import { logger } from './logger';
 
 export const Types = {
   beforeLogin: 'beforeLogin',
+  afterLogin: 'afterLogin',
   afterLogout: 'afterLogout',
   beforeSave: 'beforeSave',
   afterSave: 'afterSave',
@@ -39,10 +40,13 @@ function validateClassNameForTriggers(className, type) {
     // TODO: Allow proper documented way of using nested increment ops
     throw 'Only afterSave is allowed on _PushStatus';
   }
-  if (type === Types.beforeLogin && className !== '_User') {
+  if (
+    (type === Types.beforeLogin || type === Types.afterLogin) &&
+    className !== '_User'
+  ) {
     // TODO: check if upstream code will handle `Error` instance rather
     // than this anti-pattern of throwing strings
-    throw 'Only the _User class is allowed for the beforeLogin trigger';
+    throw 'Only the _User class is allowed for the beforeLogin and afterLogin triggers';
   }
   if (type === Types.afterLogout && className !== '_Session') {
     // TODO: check if upstream code will handle `Error` instance rather
@@ -615,7 +619,8 @@ export function maybeRunTrigger(
         const promise = trigger(request);
         if (
           triggerType === Types.afterSave ||
-          triggerType === Types.afterDelete
+          triggerType === Types.afterDelete ||
+          triggerType === Types.afterLogin
         ) {
           logTriggerAfterHook(
             triggerType,