Merge pull request from GHSA-8w3j-g983-8jh5

* Add Test and Authenticator for GHSA-8w3j-g983-8jh5

* fix for GHSA-8w3j-g983-8jh5

* nit whitespace

not sure why lint isn't catching...

Author: fastrde

Diff for: spec/ParseUser.spec.js

@@ -3847,4 +3847,41 @@ describe('Parse.User testing', () => {
       }
     );
   });
+
+  it('should validate credentials first and check if account already linked afterwards (GHSA-8w3j-g983-8jh5)', async done => {
+    // Add User to Database with authData
+    const database = Config.get(Parse.applicationId).database;
+    const collection = await database.adapter._adaptiveCollection('_User');
+    await collection.insertOne({
+      _id: 'ABCDEF1234',
+      name: '<some_name>',
+      email: '<some_email>',
+      username: '<some_username>',
+      _hashed_password: '<some_password>',
+      _auth_data_custom: {
+        id: 'linkedID', // Already linked userid
+      },
+      sessionToken: '<some_session_token>',
+    });
+    const provider = {
+      getAuthType: () => 'custom',
+      restoreAuthentication: () => true,
+    }; // AuthProvider checks if password is 'password'
+    Parse.User._registerAuthenticationProvider(provider);
+
+    // Try to link second user with wrong password
+    try {
+      const user = await Parse.AnonymousUtils.logIn();
+      await user._linkWith(provider.getAuthType(), {
+        authData: { id: 'linkedID', password: 'wrong' },
+      });
+    } catch (error) {
+      // This should throw Parse.Error.SESSION_MISSING and not Parse.Error.ACCOUNT_ALREADY_LINKED
+      expect(error.code).toEqual(Parse.Error.SESSION_MISSING);
+      done();
+      return;
+    }
+    fail();
+    done();
+  });
 });

Diff for: spec/helper.js

@@ -118,6 +118,7 @@ const defaultConfiguration = {
   },
   auth: {
     // Override the facebook provider
+    custom: mockCustom(),
     facebook: mockFacebook(),
     myoauth: {
       module: path.resolve(__dirname, 'myoauth'), // relative path as it's run from src
@@ -348,6 +349,24 @@ function range(n) {
   return answer;
 }
 
+function mockCustomAuthenticator(id, password) {
+  const custom = {};
+  custom.validateAuthData = function(authData) {
+    if (authData.id === id && authData.password.startsWith(password)) {
+      return Promise.resolve();
+    }
+    throw new Parse.Error(Parse.Error.OBJECT_NOT_FOUND, 'not validated');
+  };
+  custom.validateAppId = function() {
+    return Promise.resolve();
+  };
+  return custom;
+}
+
+function mockCustom() {
+  return mockCustomAuthenticator('fastrde', 'password');
+}
+
 function mockFacebookAuthenticator(id, token) {
   const facebook = {};
   facebook.validateAuthData = function(authData) {
@@ -406,6 +425,7 @@ global.jequal = jequal;
 global.range = range;
 global.reconfigureServer = reconfigureServer;
 global.defaultConfiguration = defaultConfiguration;
+global.mockCustomAuthenticator = mockCustomAuthenticator;
 global.mockFacebookAuthenticator = mockFacebookAuthenticator;
 global.jfail = function(err) {
   fail(JSON.stringify(err));

Diff for: src/RestWrite.js

@@ -449,17 +449,10 @@ RestWrite.prototype.handleAuthData = function(authData) {
   let results;
   return this.findUsersWithAuthData(authData).then(async r => {
     results = this.filteredObjectsByACL(r);
-    if (results.length > 1) {
-      // More than 1 user with the passed id's
-      throw new Parse.Error(
-        Parse.Error.ACCOUNT_ALREADY_LINKED,
-        'this auth is already used'
-      );
-    }
 
-    this.storage['authProvider'] = Object.keys(authData).join(',');
+    if (results.length == 1) {
+      this.storage['authProvider'] = Object.keys(authData).join(',');
 
-    if (results.length > 0) {
       const userResult = results[0];
       const mutatedAuthData = {};
       Object.keys(authData).forEach(provider => {
@@ -543,7 +536,15 @@ RestWrite.prototype.handleAuthData = function(authData) {
         }
       }
     }
-    return this.handleAuthDataValidation(authData);
+    return this.handleAuthDataValidation(authData).then(() => {
+      if (results.length > 1) {
+        // More than 1 user with the passed id's
+        throw new Parse.Error(
+          Parse.Error.ACCOUNT_ALREADY_LINKED,
+          'this auth is already used'
+        );
+      }
+    });
   });
 };