Fix ScalarAuthClient to refresh tokens if they fail

Also add a test to make sure it does it

src/ScalarAuthClient.js

@@ -51,7 +51,7 @@ class ScalarAuthClient {
         return this.scalarToken != null; // undef or null
     }
 
-    // Returns a scalar_token string
+    // Returns a promise that resolves to a scalar_token string
     getScalarToken() {
         let token = this.scalarToken;
         if (!token) token = window.localStorage.getItem("mx_scalar_token");
@@ -59,7 +59,9 @@ class ScalarAuthClient {
         if (!token) {
             return this.registerForToken();
         } else {
-            return this._checkToken(token);
+            return this._checkToken(token).catch(() => {
+                return this.registerForToken();
+            });
         }
     }
 
@@ -105,6 +107,8 @@ class ScalarAuthClient {
                 )]).then(() => {
                     return token;
                 });
+            } else {
+                throw e;
             }
         });
     }

test/ScalarAuthClient-test.js

@@ -0,0 +1,57 @@
+/*
+Copyright 2019 The Matrix.org Foundation C.I.C.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+import expect from 'expect';
+
+import sinon from 'sinon';
+
+import ScalarAuthClient from '../src/ScalarAuthClient';
+import MatrixClientPeg from '../src/MatrixClientPeg';
+import { stubClient } from './test-utils';
+
+describe('ScalarAuthClient', function() {
+    let clientSandbox;
+    let sac;
+
+    beforeEach(function() {
+        sinon.stub(window.localStorage, 'getItem').withArgs('mx_scalar_token').returns('brokentoken');
+        clientSandbox = stubClient();
+    });
+
+    afterEach(function() {
+        clientSandbox.restore();
+        sinon.restore();
+    });
+
+    it('should request a new token if the old one fails', async function() {
+        const sac = new ScalarAuthClient();
+
+        sac._getAccountName = sinon.stub();
+        sac._getAccountName.withArgs('brokentoken').rejects({
+            message: "Invalid token",
+        });
+        sac._getAccountName.withArgs('wokentoken').resolves(MatrixClientPeg.get().getUserId());
+
+        MatrixClientPeg.get().getOpenIdToken = sinon.stub().resolves('this is your openid token');
+
+        sac.exchangeForScalarToken = sinon.stub().withArgs('this is your openid token').resolves('wokentoken');
+
+        await sac.connect();
+
+        expect(sac.exchangeForScalarToken.calledWith('this is your openid token')).toBeTruthy();
+        expect(sac.scalarToken).toEqual('wokentoken');
+    });
+});