Add external auth (#1621)

* Add external auth

* Lint

* Warn when external auth not present

src/common/auth/external_auth.js

@@ -0,0 +1,46 @@
+/**
+ * Auth class that connects to a native app for authentication.
+ */
+import { Auth } from 'home-assistant-js-websocket';
+
+const CALLBACK_METHOD = 'externalAuthSetToken';
+
+if (!window.externalApp && !window.webkit) {
+  throw new Error('External auth requires either externalApp or webkit defined on Window object.');
+}
+
+export default class ExternalAuth extends Auth {
+  constructor(hassUrl) {
+    super();
+
+    this.data = {
+      hassUrl,
+      access_token: '',
+      // This will trigger connection to do a refresh right away
+      expires: 0,
+    };
+  }
+
+  async refreshAccessToken() {
+    const meth = window.externalApp ?
+      window.externalApp.getExternalAuth :
+      window.webkit.messageHandlers.getExternalAuth.postMessage;
+
+    const responseProm = new Promise((resolve) => { window[CALLBACK_METHOD] = resolve; });
+
+    // Allow promise to set resolve on window object.
+    await 0;
+
+    meth({ callback: CALLBACK_METHOD });
+
+    // Response we expect back:
+    // {
+    //   "access_token": "qwere",
+    //   "expires_in": 1800
+    // }
+    const tokens = await responseProm;
+
+    this.data.access_token = tokens.access_token;
+    this.data.expires = (tokens.expires_in * 1000) + Date.now();
+  }
+}

src/entrypoints/core.js

@@ -11,11 +11,18 @@ import { subscribePanels } from '../data/ws-panels.js';
 import { subscribeThemes } from '../data/ws-themes.js';
 import { subscribeUser } from '../data/ws-user.js';
 
-window.hassAuth = getAuth({
-  hassUrl: `${location.protocol}//${location.host}`,
-  saveTokens,
-  loadTokens: () => Promise.resolve(loadTokens()),
-});
+const hassUrl = `${location.protocol}//${location.host}`;
+
+if (location.search.includes('external_auth=1')) {
+  window.hassAuth = import('../common/auth/external_auth.js')
+    .then(mod => new mod.default(hassUrl));
+} else {
+  window.hassAuth = getAuth({
+    hassUrl,
+    saveTokens,
+    loadTokens: () => Promise.resolve(loadTokens()),
+  });
+}
 
 window.hassConnection = window.hassAuth.then((auth) => {
   if (location.search.includes('auth_callback=1')) {