Don't sign in user when trying to connect a social account that was already created

website/common/locales/en/front.json

@@ -133,6 +133,7 @@
   "unsupportedNetwork": "This network is not currently supported.",
   "cantDetachSocial": "Account lacks another authentication method; can't detach this authentication method.",
   "onlySocialAttachLocal": "Local authentication can be added to only a social account.",
+  "socialAlreadyExists": "This social login is already linked to an existing Habitica account.",
   "invalidReqParams": "Invalid request parameters.",
   "memberIdRequired": "\"member\" must be a valid UUID.",
   "heroIdRequired": "\"heroId\" must be a valid UUID.",

website/server/libs/auth/social.js

@@ -1,6 +1,6 @@
 import passport from 'passport';
 import common from '../../../common';
-import { BadRequest } from '../errors';
+import { BadRequest, NotAuthorized } from '../errors';
 import logger from '../logger';
 import {
   generateUsername,
@@ -47,6 +47,9 @@ export async function loginSocial (req, res) { // eslint-disable-line import/pre
 
   // User already signed up
   if (user) {
+    if (existingUser) {
+      throw new NotAuthorized(res.t('socialAlreadyExists'))
+    }
     return loginRes(user, req, res);
   }