Add tests for OAuth authentication

These tests stub the $http service rather than relying on the mock
$httpBackend from Angular mocks because that makes it easier to work
with native Promises.

src/sidebar/test/oauth-auth-test.js

+'use strict';
+
+var authService = require('../oauth-auth');
+
+var DEFAULT_TOKEN_EXPIRES_IN_SECS = 1000;
+
+describe('oauth auth', function () {
+
+  var auth;
+  var clock;
+  var fakeHttp;
+  var fakeSettings;
+
+  beforeEach(function () {
+    clock = sinon.useFakeTimers();
+
+    fakeHttp = {
+      post: sinon.stub().returns(Promise.resolve({
+        status: 200,
+        data: {
+          access_token: 'an-access-token',
+          expires_in: DEFAULT_TOKEN_EXPIRES_IN_SECS,
+        },
+      })),
+    };
+
+    fakeSettings = {
+      apiUrl: 'https://hypothes.is/api/',
+      services: [{
+        authority: 'publisher.org',
+        grantToken: 'a.jwt.token',
+      }],
+    };
+
+    auth = authService(fakeHttp, fakeSettings);
+  });
+
+  afterEach(function () {
+    clock.restore();
+  });
+
+  describe('#tokenGetter', function () {
+    it('should request an access token if a grant token was provided', function () {
+      return auth.tokenGetter().then(function (token) {
+        var expectedBody =
+          'assertion=a.jwt.token' +
+          '&grant_type=urn%3Aietf%3Aparams%3Aoauth%3Agrant-type%3Ajwt-bearer';
+        assert.calledWith(fakeHttp.post, 'https://hypothes.is/api/token', expectedBody, {
+          headers: {'Content-Type': 'application/x-www-form-urlencoded'},
+        });
+        assert.equal(token, 'an-access-token');
+      });
+    });
+
+    it('should cache tokens for future use', function () {
+      return auth.tokenGetter().then(function () {
+        fakeHttp.post.reset();
+        return auth.tokenGetter();
+      }).then(function (token) {
+        assert.equal(token, 'an-access-token');
+        assert.notCalled(fakeHttp.post);
+      });
+    });
+
+    it('should return null if no grant token was provided', function () {
+      var auth = authService(fakeHttp, {
+        services: [{authority: 'publisher.org'}],
+      });
+      return auth.tokenGetter().then(function (token) {
+        assert.notCalled(fakeHttp.post);
+        assert.equal(token, null);
+      });
+    });
+
+    it('should refresh the access token if it has expired', function () {
+      return auth.tokenGetter().then(function () {
+        clock.tick(DEFAULT_TOKEN_EXPIRES_IN_SECS * 1000 + 100);
+        fakeHttp.post.returns(Promise.resolve({
+          status: 200,
+          data: {
+            access_token: 'a-different-access-token',
+            expires_in: DEFAULT_TOKEN_EXPIRES_IN_SECS,
+          },
+        }));
+        return auth.tokenGetter();
+      }).then(function (token) {
+        assert.equal(token, 'a-different-access-token');
+      });
+    });
+  });
+
+  describe('#clearCache', function () {
+    it('should clear cached tokens', function () {
+      return auth.tokenGetter().then(function () {
+        fakeHttp.post.reset();
+        auth.clearCache();
+        return auth.tokenGetter();
+      }).then(function () {
+        assert.calledOnce(fakeHttp.post);
+      });
+    });
+  });
+});