Auth First Run (#1207)

Co-authored-by: Tommaso Sciortino <sciortino@gmail.com>
Co-authored-by: N. Taylor Mullen <ntaylormullen@google.com>

packages/cli/src/config/auth.ts

@@ -0,0 +1,44 @@
+/**
+ * @license
+ * Copyright 2025 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+import { AuthType } from '@gemini-cli/core';
+import { loadEnvironment } from './config.js';
+
+export const validateAuthMethod = (authMethod: string): string | null => {
+  loadEnvironment();
+  if (authMethod === AuthType.LOGIN_WITH_GOOGLE_PERSONAL) {
+    return null;
+  }
+
+  if (authMethod === AuthType.LOGIN_WITH_GOOGLE_ENTERPRISE) {
+    if (!process.env.GOOGLE_CLOUD_PROJECT) {
+      return 'GOOGLE_CLOUD_PROJECT environment variable not found. Add that to your .env and try again, no reload needed!';
+    }
+    return null;
+  }
+
+  if (authMethod === AuthType.USE_GEMINI) {
+    if (!process.env.GEMINI_API_KEY) {
+      return 'GEMINI_API_KEY environment variable not found. Add that to your .env and try again, no reload needed!';
+    }
+    return null;
+  }
+
+  if (authMethod === AuthType.USE_VERTEX_AI) {
+    if (!process.env.GOOGLE_API_KEY) {
+      return 'GOOGLE_API_KEY environment variable not found. Add that to your .env and try again, no reload needed!';
+    }
+    if (!process.env.GOOGLE_CLOUD_PROJECT) {
+      return 'GOOGLE_CLOUD_PROJECT environment variable not found. Add that to your .env and try again, no reload needed!';
+    }
+    if (!process.env.GOOGLE_CLOUD_LOCATION) {
+      return 'GOOGLE_CLOUD_LOCATION environment variable not found. Add that to your .env and try again, no reload needed!';
+    }
+    return null;
+  }
+
+  return 'Invalid auth method selected.';
+};