feat: load Google 3D with short-lived server tokens

Without a browser key, the app asks its server for a short-lived Google
access token (GET /api/google/tiles-token, answering accessToken and
expiresAt) and loads Photorealistic 3D Tiles directly with it as a
header. A tile refused for an expired token gets a renewed one and is
retried once. A server that does not offer tokens changes nothing: the
app continues through ion or the keyless globe as before.

src/maps/google3d.js

@@ -16,30 +16,43 @@ export function selectMapStartupRoute({
 
 /**
  * Load Google Photorealistic 3D Tiles through direct Google access when
- * configured, otherwise through Cesium ion's hosted Google asset. If the
- * direct request fails and an ion token is available, ion is the recovery path.
+ * configured, otherwise through Cesium ion's hosted Google asset. Direct
+ * access uses a browser key, or else short-lived tokens from the app's
+ * server (see googleTokens.js). If direct access fails and an ion token is
+ * available, ion is the recovery path.
  *
  * @param {object} Cesium
- * @param {{googleApiKey?: string, cesiumToken?: string}} credentials
- * @returns {Promise<{tileset: object|null, route: 'google-direct'|'google-ion'|'osm', errors: Error[]}>}
+ * @param {{googleApiKey?: string, cesiumToken?: string, googleTokens?: {token: Function}|null}} credentials
+ * @returns {Promise<{tileset: object|null, route: 'google-direct'|'google-token'|'google-ion'|'osm', errors: Error[]}>}
  */
 export async function loadPhotorealisticTileset(
   Cesium,
-  { googleApiKey = '', cesiumToken = '' } = {},
+  { googleApiKey = '', cesiumToken = '', googleTokens = null } = {},
 ) {
   const googleKey = clean(googleApiKey);
   const ionToken = clean(cesiumToken);
   const errors = [];
 
   const attempts = [];
-  if (googleKey) attempts.push({ route: 'google-direct', googleKey });
-  if (ionToken) attempts.push({ route: 'google-ion', googleKey: undefined });
+  if (googleKey)
+    attempts.push({
+      route: 'google-direct',
+      create: () => createGoogleDirectTileset(Cesium, googleKey),
+    });
+  else if (googleTokens)
+    attempts.push({
+      route: 'google-token',
+      create: () => createGoogleTokenTileset(Cesium, googleTokens),
+    });
+  if (ionToken)
+    attempts.push({
+      route: 'google-ion',
+      create: () => createGoogleIonTileset(Cesium, ionToken),
+    });
 
   for (const attempt of attempts) {
     try {
-      const tileset = attempt.googleKey
-        ? await createGoogleDirectTileset(Cesium, attempt.googleKey)
-        : await createGoogleIonTileset(Cesium, ionToken);
+      const tileset = await attempt.create();
       return { tileset, route: attempt.route, errors };
     } catch (error) {
       errors.push(error instanceof Error ? error : new Error(String(error)));
@@ -60,6 +73,39 @@ export function createGoogleDirectTileset(Cesium, key) {
   );
 }
 
+/**
+ * Google 3D with short-lived tokens instead of a key. Every tile request
+ * carries the token as a header; a tile refused for an expired token gets
+ * the renewed one and is tried once more.
+ */
+export async function createGoogleTokenTileset(Cesium, tokens) {
+  const token = await tokens.token();
+  if (!token) throw new Error('Google 3D tokens are not offered');
+  const credit = Cesium.GoogleMaps.getDefaultCredit?.();
+  const resource = new Cesium.Resource({
+    url: `${Cesium.GoogleMaps.mapTilesApiEndpoint}v1/3dtiles/root.json`,
+    headers: { Authorization: `Bearer ${token}` },
+    credits: credit ? [credit] : undefined,
+    retryAttempts: 1,
+    async retryCallback(failed, error) {
+      if (![401, 403].includes(error?.statusCode)) return false;
+      const used = failed.headers.Authorization?.replace(/^Bearer /, '');
+      const renewed = await tokens.token({ replacing: used });
+      if (!renewed || renewed === used) return false;
+      failed.headers.Authorization = `Bearer ${renewed}`;
+      return true;
+    },
+  });
+  // The settings Cesium's Google helper applies to the key route.
+  return Cesium.Cesium3DTileset.fromUrl(resource, {
+    cacheBytes: 1536 * 1024 * 1024,
+    maximumCacheOverflowBytes: 1024 * 1024 * 1024,
+    enableCollision: true,
+    // Tiles keep drawing their own texture while draped weather loads.
+    asynchronouslyLoadImagery: true,
+  });
+}
+
 export async function createGoogleIonTileset(
   Cesium,
   accessToken,