added afterLogout trigger (#6217)

* added afterLogout trigger

* added verification of session object in tests

* removed obsolete code

* removed unsued code

* improved tests to verify user ID

src/Routers/UsersRouter.js

@@ -302,6 +302,7 @@ export class UsersRouter extends ClassesRouter {
                 records.results[0].objectId
               )
               .then(() => {
+                this._runAfterLogoutTrigger(req, records.results[0]);
                 return Promise.resolve(success);
               });
           }
@@ -311,6 +312,17 @@ export class UsersRouter extends ClassesRouter {
     return Promise.resolve(success);
   }
 
+  _runAfterLogoutTrigger(req, session) {
+    // After logout trigger
+    maybeRunTrigger(
+      TriggerTypes.afterLogout,
+      req.auth,
+      Parse.Session.fromJSON(Object.assign({ className: '_Session' }, session)),
+      null,
+      req.config
+    );
+  }
+
   _throwOnBadEmailConfig(req) {
     try {
       Config.validateEmailConfiguration({

src/cloud-code/Parse.Cloud.js

@@ -165,6 +165,41 @@ ParseCloud.beforeLogin = function(handler) {
   );
 };
 
+/**
+ *
+ * Registers the after logout function.
+ *
+ * **Available in Cloud Code only.**
+ *
+ * This function is triggered after a user logs out.
+ *
+ * ```
+ * Parse.Cloud.afterLogout((request) => {
+ *   // code here
+ * })
+ *
+ * ```
+ *
+ * @method afterLogout
+ * @name Parse.Cloud.afterLogout
+ * @param {Function} func The function to run after a logout. This function can be async and should take one parameter a {@link Parse.Cloud.TriggerRequest};
+ */
+ParseCloud.afterLogout = function(handler) {
+  let className = '_Session';
+  if (typeof handler === 'string' || isParseObjectConstructor(handler)) {
+    // validation will occur downstream, this is to maintain internal
+    // code consistency with the other hook types.
+    className = getClassName(handler);
+    handler = arguments[1];
+  }
+  triggers.addTrigger(
+    triggers.Types.afterLogout,
+    className,
+    handler,
+    Parse.applicationId
+  );
+};
+
 /**
  * Registers an after save function.
  *

src/triggers.js

@@ -4,6 +4,7 @@ import { logger } from './logger';
 
 export const Types = {
   beforeLogin: 'beforeLogin',
+  afterLogout: 'afterLogout',
   beforeSave: 'beforeSave',
   afterSave: 'afterSave',
   beforeDelete: 'beforeDelete',
@@ -32,10 +33,6 @@ const baseStore = function() {
 };
 
 function validateClassNameForTriggers(className, type) {
-  const restrictedClassNames = ['_Session'];
-  if (restrictedClassNames.indexOf(className) != -1) {
-    throw `Triggers are not supported for ${className} class.`;
-  }
   if (type == Types.beforeSave && className === '_PushStatus') {
     // _PushStatus uses undocumented nested key increment ops
     // allowing beforeSave would mess up the objects big time
@@ -47,6 +44,16 @@ function validateClassNameForTriggers(className, type) {
     // than this anti-pattern of throwing strings
     throw 'Only the _User class is allowed for the beforeLogin trigger';
   }
+  if (type === Types.afterLogout && className !== '_Session') {
+    // TODO: check if upstream code will handle `Error` instance rather
+    // than this anti-pattern of throwing strings
+    throw 'Only the _Session class is allowed for the afterLogout trigger.';
+  }
+  if (className === '_Session' && type !== Types.afterLogout) {
+    // TODO: check if upstream code will handle `Error` instance rather
+    // than this anti-pattern of throwing strings
+    throw 'Only the afterLogout trigger is allowed for the _Session class.';
+  }
   return className;
 }