Improve Auth error messaging (#1358)

packages/core/src/utils/errors.ts

@@ -4,6 +4,8 @@
  * SPDX-License-Identifier: Apache-2.0
  */
 
+import { GaxiosError } from 'gaxios';
+
 export function isNodeError(error: unknown): error is NodeJS.ErrnoException {
   return error instanceof Error && 'code' in error;
 }
@@ -11,12 +13,50 @@ export function isNodeError(error: unknown): error is NodeJS.ErrnoException {
 export function getErrorMessage(error: unknown): string {
   if (error instanceof Error) {
     return error.message;
-  } else {
-    try {
-      const errorMessage = String(error);
-      return errorMessage;
-    } catch {
-      return 'Failed to get error details';
-    }
+  }
+  try {
+    return String(error);
+  } catch {
+    return 'Failed to get error details';
   }
 }
+
+export class ForbiddenError extends Error {}
+export class UnauthorizedError extends Error {}
+export class BadRequestError extends Error {}
+
+interface ResponseData {
+  error?: {
+    code?: number;
+    message?: string;
+  };
+}
+
+export function toFriendlyError(error: unknown): unknown {
+  if (error instanceof GaxiosError) {
+    const data = parseResponseData(error);
+    if (data.error && data.error.message && data.error.code) {
+      switch (data.error.code) {
+        case 400:
+          return new BadRequestError(data.error.message);
+        case 401:
+          return new UnauthorizedError(data.error.message);
+        case 403:
+          // It's import to pass the message here since it might
+          // explain the cause like "the cloud project you're
+          // using doesn't have code assist enabled".
+          return new ForbiddenError(data.error.message);
+        default:
+      }
+    }
+  }
+  return error;
+}
+
+function parseResponseData(error: GaxiosError): ResponseData {
+  // Inexplicably, Gaxios sometimes doesn't JSONify the response data.
+  if (typeof error.response?.data === 'string') {
+    return JSON.parse(error.response?.data) as ResponseData;
+  }
+  return typeof error.response?.data as ResponseData;
+}