Customizing refresh token flow

Departs from oauth2, oh well. Fixes #58.

app/authenticators/oauth2.js

@@ -1,6 +1,69 @@
 import OAuth2PasswordGrant from 'ember-simple-auth/authenticators/oauth2-password-grant';
 import config from '../config/environment';
+import parseBase64 from '../utils/parse-base64';
+const { RSVP: { Promise }, isEmpty, run, Logger: { warn } } = Ember;
 
 export default OAuth2PasswordGrant.extend({
   serverTokenEndpoint: `${config.apiURL}/api/authenticate`,
+  serverTokenRefreshEndpoint: `${config.apiURL}/api/refresh`,
+
+  authenticate: function(identification, password, scope = []) {
+    return new Promise((resolve, reject) => {
+      const data = { username: identification, password };
+      const serverTokenEndpoint = this.get('serverTokenEndpoint');
+      this.makeRequest(serverTokenEndpoint, data).then((response) => {
+        run(() => {
+          const token = parseBase64(response['access_token']);
+          const expiresAt = this._absolutizeExpirationTime(token['exp']);
+          this._scheduleAccessTokenRefresh(expiresAt, response['access_token']);
+          if (!isEmpty(expiresAt)) {
+            response = Ember.merge(response, { 'expires_at': expiresAt });
+          }
+          resolve(response);
+        });
+      }, (xhr) => {
+        run(null, reject, xhr.responseJSON || xhr.responseText);
+      });
+    });
+  },
+
+  _scheduleAccessTokenRefresh: function(expiresAt, accessToken) {
+    if (this.get('refreshAccessTokens')) {
+      const now = (new Date()).getTime();
+      const offset = (Math.floor(Math.random() * 5) + 5) * 1000;
+      if (!isEmpty(accessToken) && !isEmpty(expiresAt) && expiresAt > now - offset) {
+        run.cancel(this._refreshTokenTimeout);
+        delete this._refreshTokenTimeout;
+        if (!Ember.testing) {
+          this._refreshTokenTimeout = run.later(this, this._refreshAccessToken, expiresAt, accessToken, expiresAt - now - offset);
+        }
+      }
+    }
+  },
+
+  _refreshAccessToken: function(expiresAt, accessToken) {
+    const data = { 'token': accessToken };
+    const serverTokenRefreshEndpoint = this.get('serverTokenRefreshEndpoint');
+    return new Promise((resolve, reject) => {
+      this.makeRequest(serverTokenRefreshEndpoint, data).then((response) => {
+        run(() => {
+          const token = parseBase64(response['access_token']);
+          const expiresAt = this._absolutizeExpirationTime(token['exp']);
+          const data = Ember.merge(response, { 'expires_at': expiresAt });
+          this._scheduleAccessTokenRefresh(expiresAt, response['access_token']);
+          this.trigger('sessionDataUpdated', data);
+          resolve(data);
+        });
+      }, (xhr, status, error) => {
+        warn(`Access token could not be refreshed - server responded with ${error}.`);
+        reject();
+      });
+    });
+  },
+
+  _absolutizeExpirationTime: function(expiresAt) {
+    if (!isEmpty(expiresAt)) {
+      return new Date(expiresAt * 1000).getTime();
+    }
+  }
 });