feat: Add support for Vertex AI and Vertex express mode (#380)

README.md

@@ -8,19 +8,46 @@ For more comprehensive documentation, please see the [full documentation here](.
 
 ## Setup
 
-1.  **Get a Gemini API Key:** Obtain your API key from Google AI Studio: [https://aistudio.google.com/app/apikey](https://aistudio.google.com/app/apikey)
-2.  **Set Environment Variable:** Set the `GEMINI_API_KEY` environment variable to your obtained key. You can do this temporarily in your current shell session:
-    ```bash
-    export GEMINI_API_KEY="YOUR_API_KEY"
-    ```
-    Or add it to your shell's configuration file (like `~/.bashrc`, `~/.zshrc`, or `~/.profile`) for persistence:
-    ```bash
-    echo 'export GEMINI_API_KEY="YOUR_API_KEY"' >> ~/.bashrc # Or your preferred shell config file
-    source ~/.bashrc # Reload the config
-    ```
-    Replace `"YOUR_API_KEY"` with your actual key.
-3.  **Install the Gemini CLI:**
-    _(Instructions for installing the CLI will be added here once packaging is finalized. For now, if you have access to the source code, you can run it directly after building the project as described below.)_
+The Gemini CLI supports several ways to authenticate with Google's AI services. You'll need to configure **one** of the following methods:
+
+1.  **Gemini API Key:**
+
+    - Obtain your API key from Google AI Studio: [https://aistudio.google.com/app/apikey](https://aistudio.google.com/app/apikey)
+    - Set the `GEMINI_API_KEY` environment variable. You can do this temporarily in your current shell session:
+      ```bash
+      export GEMINI_API_KEY="YOUR_GEMINI_API_KEY"
+      ```
+      Or add it to your shell's configuration file (like `~/.bashrc`, `~/.zshrc`, or `~/.profile`) for persistence:
+      ```bash
+      echo 'export GEMINI_API_KEY="YOUR_GEMINI_API_KEY"' >> ~/.bashrc # Or your preferred shell config file
+      source ~/.bashrc # Reload the config
+      ```
+      Replace `"YOUR_GEMINI_API_KEY"` with your actual key.
+
+2.  **Google API Key (Vertex AI Express Mode):**
+
+    - This key can be a general Google Cloud API key enabled for the Gemini API or Vertex AI.
+    - Set the `GOOGLE_API_KEY` and `GOOGLE_GENAI_USE_VERTEXAI` environment variables:
+      ```bash
+      export GOOGLE_API_KEY="YOUR_GOOGLE_API_KEY"
+      export GOOGLE_GENAI_USE_VERTEXAI=true
+      ```
+
+3.  **Vertex AI (Project and Location):**
+    - Ensure you have a Google Cloud Project and have enabled the Vertex AI API.
+    - Set up Application Default Credentials (ADC). For more details, refer to the [official Google Cloud ADC documentation](https://cloud.google.com/docs/authentication/provide-credentials-adc):
+      ```bash
+      gcloud auth application-default login
+      ```
+    - Set the `GOOGLE_CLOUD_PROJECT`, `GOOGLE_CLOUD_LOCATION`, and `GOOGLE_GENAI_USE_VERTEXAI` environment variables:
+      ```bash
+      export GOOGLE_CLOUD_PROJECT="YOUR_PROJECT_ID"
+      export GOOGLE_CLOUD_LOCATION="YOUR_PROJECT_LOCATION" # e.g., us-central1
+      export GOOGLE_GENAI_USE_VERTEXAI=true
+      ```
+
+**Install the Gemini CLI:**
+_(Instructions for installing the CLI will be added here once packaging is finalized. For now, if you have access to the source code, you can run it directly after building the project as described elsewhere.)_
 
 ## Building (for contributors)
 

packages/cli/src/config/config.ts

@@ -354,11 +354,25 @@ export async function loadCliConfig(settings: Settings): Promise<Config> {
   // Load .env file using logic from server package
   loadEnvironment();
 
-  // Check API key (CLI responsibility)
-  if (!process.env.GEMINI_API_KEY) {
+  const geminiApiKey = process.env.GEMINI_API_KEY;
+  const googleApiKey = process.env.GOOGLE_API_KEY;
+  const googleCloudProject = process.env.GOOGLE_CLOUD_PROJECT;
+  const googleCloudLocation = process.env.GOOGLE_CLOUD_LOCATION;
+
+  const hasGeminiApiKey = !!geminiApiKey;
+  const hasGoogleApiKey = !!googleApiKey;
+  const hasVertexProjectLocationConfig =
+    !!googleCloudProject && !!googleCloudLocation;
+
+  if (!hasGeminiApiKey && !hasGoogleApiKey && !hasVertexProjectLocationConfig) {
     logger.error(
-      'GEMINI_API_KEY is not set. See https://ai.google.dev/gemini-api/docs/api-key to obtain one. ' +
-        'Please set it in your .env file or as an environment variable.',
+      'No valid API authentication configuration found. Please set ONE of the following combinations in your environment variables or .env file:\n' +
+        '1. GEMINI_API_KEY (for Gemini API access).\n' +
+        '2. GOOGLE_API_KEY (for Gemini API or Vertex AI Express Mode access).\n' +
+        '3. GOOGLE_CLOUD_PROJECT and GOOGLE_CLOUD_LOCATION (for Vertex AI access).\n\n' +
+        'For Gemini API keys, visit: https://ai.google.dev/gemini-api/docs/api-key\n' +
+        'For Vertex AI authentication, visit: https://cloud.google.com/vertex-ai/docs/start/authentication\n' +
+        'The GOOGLE_GENAI_USE_VERTEXAI environment variable can also be set to true/false to influence service selection when ambiguity exists.',
     );
     process.exit(1);
   }
@@ -373,9 +387,12 @@ export async function loadCliConfig(settings: Settings): Promise<Config> {
 
   const userAgent = await createUserAgent();
 
+  // Gemini Developer API or GCP Express or Vertex AI
+  const apiKeyForServer = geminiApiKey || googleApiKey || '';
+
   // Create config using factory from server package
   return createServerConfig(
-    process.env.GEMINI_API_KEY,
+    apiKeyForServer,
     argv.model || DEFAULT_GEMINI_MODEL,
     argv.sandbox ?? settings.sandbox ?? false,
     process.cwd(),

packages/server/src/core/client.ts

@@ -35,8 +35,9 @@ export class GeminiClient {
 
   constructor(private config: Config) {
     const userAgent = config.getUserAgent();
+    const apiKeyFromConfig = config.getApiKey();
     this.client = new GoogleGenAI({
-      apiKey: config.getApiKey(),
+      apiKey: apiKeyFromConfig === '' ? undefined : apiKeyFromConfig,
       httpOptions: {
         headers: {
           'User-Agent': userAgent,