Ensure generic data is returned after Torii.fetch (#1310)

Previously, generic `sessionData` was being clobbered be the data returned by Torii.fetch.
Now, generic sessionData is preserved and the result of Torii.fetch is merged into it.

addon/authenticators/torii.js

@@ -1,6 +1,7 @@
 import RSVP from 'rsvp';
 import { assert } from '@ember/debug';
 import { isPresent, isEmpty } from '@ember/utils';
+import { assign as emberAssign } from '@ember/polyfills';
 import BaseAuthenticator from './base';
 
 /**
@@ -58,9 +59,9 @@ export default BaseAuthenticator.extend({
     if (!isEmpty(data.provider)) {
       const { provider } = data;
 
-      return this.get('torii').fetch(data.provider, data).then((data) => {
-        this._authenticateWithProvider(provider, data);
-        return data;
+      return this.get('torii').fetch(data.provider, data).then((fetchedData) => {
+        this._authenticateWithProvider(provider, fetchedData);
+        return emberAssign(data, fetchedData);
       }, () => delete this._provider);
     } else {
       delete this._provider;

tests/unit/authenticators/torii-test.js

@@ -40,9 +40,9 @@ describe('ToriiAuthenticator', () => {
           sinon.stub(torii, 'fetch').returns(RSVP.resolve({ some: 'other data' }));
         });
 
-        it('returns a promise that resolves with the session data', function() {
-          return authenticator.restore({ some: 'data', provider: 'provider' }).then((data) => {
-            expect(data).to.eql({ some: 'other data', provider: 'provider' });
+        it('returns a promise that resolves with the session data merged with the data fetched from torri', function() {
+          return authenticator.restore({ some: 'data', provider: 'provider', another: 'prop' }).then((data) => {
+            expect(data).to.eql({ some: 'other data', provider: 'provider', another: 'prop' });
           });
         });
       });