fix: remove placeholder cache attribute of access token

PiperOrigin-RevId: 593849437

Author: yyyu-google

src/index.ts

@@ -65,7 +65,6 @@ export class VertexAI_Preview {
   protected googleAuth: GoogleAuth = new GoogleAuth({
     scopes: 'https://www.googleapis.com/auth/cloud-platform',
   });
-  private tokenInternalPromise?: Promise<any>;
 
   /**
    * @constructor
@@ -90,9 +89,6 @@ export class VertexAI_Preview {
    * @return {Promise<any>} Promise of token
    */
   get token(): Promise<any> {
-    if (this.tokenInternalPromise) {
-      return this.tokenInternalPromise;
-    }
     const credential_error_message = "\nUnable to authenticate your request\
         \nDepending on your run time environment, you can get authentication by\
         \n- if in local instance or cloud shell: `!gcloud auth login`\

src/index_test.ts

@@ -159,7 +159,7 @@ describe('VertexAI', () => {
       project: PROJECT,
       location: LOCATION,
     });
-    vertexai.preview['tokenInternalPromise'] = Promise.resolve(TEST_TOKEN);
+    spyOnProperty(vertexai.preview, 'token', 'get').and.resolveTo(TEST_TOKEN);
     model = vertexai.preview.getGenerativeModel({model: 'gemini-pro'});
   });
 
@@ -247,8 +247,7 @@ describe('VertexAI', () => {
         location: LOCATION,
         apiEndpoint: TEST_ENDPOINT_BASE_PATH,
       });
-      vertexaiWithBasePath.preview['tokenInternalPromise'] =
-        Promise.resolve(TEST_TOKEN);
+      spyOnProperty(vertexaiWithBasePath.preview, 'token', 'get').and.resolveTo(TEST_TOKEN);
       model = vertexaiWithBasePath.preview.getGenerativeModel({
         model: 'gemini-pro',
       });
@@ -280,8 +279,8 @@ describe('VertexAI', () => {
         project: PROJECT,
         location: LOCATION,
       });
-      vertexaiWithoutBasePath.preview['tokenInternalPromise'] =
-        Promise.resolve(TEST_TOKEN);
+      spyOnProperty(vertexaiWithoutBasePath.preview, 'token', 'get')
+          .and.resolveTo(TEST_TOKEN);
       model = vertexaiWithoutBasePath.preview.getGenerativeModel({
         model: 'gemini-pro',
       });
@@ -461,7 +460,7 @@ describe('ChatSession', () => {
 
   beforeEach(() => {
     vertexai = new VertexAI({project: PROJECT, location: LOCATION});
-    vertexai.preview['tokenInternalPromise'] = Promise.resolve(TEST_TOKEN);
+    spyOnProperty(vertexai.preview, 'token', 'get').and.resolveTo(TEST_TOKEN);
     model = vertexai.preview.getGenerativeModel({model: 'gemini-pro'});
     chatSession = model.startChat({
       history: TEST_USER_CHAT_MESSAGE,