[Identity] ManagedIdentityCredential fix (#13919)

This pull request makes the ManagedIdentityCredential:

- Treat unreachable host as we were treating unreachable network.
  - This should have been done before, but we didn't catch it.
  - I couldn't find any other error that seemed relevant to me, using this as reference: [link](606df7c4e7/deps/uv/src/win/error.c).
- Treat errors with undefined status code as if the credential was unavailable, to avoid breaking the chained token credentials in that case.
- Add tests (turns out that some where being skipped by mistake!)
- Add more comments to improve reading.

This PR:
Fixes #13894

sdk/identity/identity/CHANGELOG.md

@@ -7,6 +7,7 @@
 - `DefaultAzureCredential`'s implementation for browsers was simplified to throw a simple error instead of trying credentials that were already not supported for the browser.
 - Breaking Change: `InteractiveBrowserCredential` for the browser now requires the client ID to be provided.
 - Documentation was added to elaborate on how to configure an AAD application to support `InteractiveBrowserCredential`.
+- Bug fix: `ManagedIdentityCredential` now also properly handles `EHOSTUNREACH` errors. Fixes issue [13894](https://github.com/Azure/azure-sdk-for-js/issues/13894).
 
 ## 1.2.4-beta.1 (2021-02-12)
 

sdk/identity/identity/rollup.base.config.js

@@ -38,7 +38,8 @@ export function nodeConfig(test = false) {
     baseConfig.input = [
       "dist-esm/test/public/*.spec.js",
       "dist-esm/test/public/node/*.spec.js",
-      "dist-esm/test/internal/*.spec.js"
+      "dist-esm/test/internal/*.spec.js",
+      "dist-esm/test/internal/node/*.spec.js"
     ];
     baseConfig.plugins.unshift(multiEntry({ exports: false }));
 
@@ -97,7 +98,8 @@ export function browserConfig(test = false) {
     baseConfig.input = [
       "dist-esm/test/public/*.spec.js",
       "dist-esm/test/public/browser/*.spec.js",
-      "dist-esm/test/internal/*.spec.js"
+      "dist-esm/test/internal/*.spec.js",
+      "dist-esm/test/internal/browser/*.spec.js"
     ];
     baseConfig.plugins.unshift(multiEntry({ exports: false }));
     baseConfig.output.file = "test-browser/index.js";

sdk/identity/identity/src/credentials/managedIdentityCredential/index.ts

@@ -196,7 +196,20 @@ export class ManagedIdentityCredential implements TokenCredential {
         message: err.message
       });
 
+      // If either the network is unreachable,
+      // we can safely assume the credential is unavailable.
       if (err.code === "ENETUNREACH") {
+        const error = new CredentialUnavailable(
+          "ManagedIdentityCredential is unavailable. Network unreachable."
+        );
+
+        logger.getToken.info(formatError(scopes, error));
+        throw error;
+      }
+
+      // If either the host was unreachable,
+      // we can safely assume the credential is unavailable.
+      if (err.code === "EHOSTUNREACH") {
         const error = new CredentialUnavailable(
           "ManagedIdentityCredential is unavailable. No managed identity endpoint found."
         );
@@ -213,6 +226,15 @@ export class ManagedIdentityCredential implements TokenCredential {
         );
       }
 
+      // If the error has no status code, we can assume there was no available identity.
+      // This will throw silently during any ChainedTokenCredential.
+      if (err.statusCode === undefined) {
+        throw new CredentialUnavailable(
+          `ManagedIdentityCredential authentication failed. Message ${err.message}`
+        );
+      }
+
+      // Any other error should break the chain.
       throw new AuthenticationError(err.statusCode, {
         error: "ManagedIdentityCredential authentication failed.",
         error_description: err.message

sdk/identity/identity/test/authTestUtils.ts

@@ -14,7 +14,8 @@ import {
 import * as coreHttp from "@azure/core-http";
 
 export interface MockAuthResponse {
-  status: number;
+  status?: number;
+  error?: RestError;
   headers?: HttpHeaders;
   parsedBody?: any;
   bodyAsText?: string;
@@ -27,7 +28,7 @@ export interface MockAuthHttpClientOptions {
 
 export class MockAuthHttpClient implements HttpClient {
   private authResponses: MockAuthResponse[] = [];
-  private currentResponse: number = 0;
+  private currentResponseIndex: number = 0;
   private mockTimeout: boolean;
 
   public tokenCredentialOptions: ClientCertificateCredentialOptions;
@@ -76,13 +77,22 @@ export class MockAuthHttpClient implements HttpClient {
       throw new Error("The number of requests has exceeded the number of authResponses");
     }
 
+    const authResponse = this.authResponses[this.currentResponseIndex];
+
+    if (authResponse.error) {
+      this.currentResponseIndex++;
+      throw authResponse.error;
+    }
+
     const response = {
       request: httpRequest,
-      headers: this.authResponses[this.currentResponse].headers || new HttpHeaders(),
-      ...this.authResponses[this.currentResponse]
+      headers: authResponse.headers || new HttpHeaders(),
+      status: authResponse.status || 200,
+      parsedBody: authResponse.parsedBody,
+      bodyAsText: authResponse.bodyAsText
     };
 
-    this.currentResponse++;
+    this.currentResponseIndex++;
     return response;
   }
 }

sdk/identity/identity/test/internal/node/managedIdentityCredential.spec.ts

@@ -9,7 +9,7 @@ import {
   imdsApiVersion
 } from "../../../src/credentials/managedIdentityCredential/constants";
 import { MockAuthHttpClient, MockAuthHttpClientOptions, assertRejects } from "../../authTestUtils";
-import { WebResource, AccessToken, HttpHeaders } from "@azure/core-http";
+import { WebResource, AccessToken, HttpHeaders, RestError } from "@azure/core-http";
 import { OAuthErrorResponse } from "../../../src/client/errors";
 
 interface AuthRequestDetails {
@@ -83,7 +83,24 @@ describe("ManagedIdentityCredential", function() {
     }
   });
 
-  it("returns error when ManagedIdentityCredential authentication failed", async function() {
+  it("returns error when no MSI is available", async function() {
+    process.env.AZURE_CLIENT_ID = "errclient";
+
+    const imdsError: RestError = new RestError("Request Timeout", "REQUEST_SEND_ERROR", 408);
+    const mockHttpClient = new MockAuthHttpClient({
+      authResponse: [{ error: imdsError }]
+    });
+
+    const credential = new ManagedIdentityCredential(process.env.AZURE_CLIENT_ID, {
+      ...mockHttpClient.tokenCredentialOptions
+    });
+    await assertRejects(
+      credential.getToken("scopes"),
+      (error: AuthenticationError) => error.message.indexOf("No MSI credential available") > -1
+    );
+  });
+
+  it("an unexpected error bubbles all the way up", async function() {
     process.env.AZURE_CLIENT_ID = "errclient";
 
     const errResponse: OAuthErrorResponse = {
@@ -92,7 +109,41 @@ describe("ManagedIdentityCredential", function() {
     };
 
     const mockHttpClient = new MockAuthHttpClient({
-      authResponse: [{ status: 400, parsedBody: errResponse }]
+      authResponse: [{ status: 200 }, { status: 500, parsedBody: errResponse }]
+    });
+
+    const credential = new ManagedIdentityCredential(process.env.AZURE_CLIENT_ID, {
+      ...mockHttpClient.tokenCredentialOptions
+    });
+    await assertRejects(
+      credential.getToken("scopes"),
+      (error: AuthenticationError) => error.message.indexOf(errResponse.error) > -1
+    );
+  });
+
+  it("returns expected error when the network was unreachable", async function() {
+    process.env.AZURE_CLIENT_ID = "errclient";
+
+    const netError: RestError = new RestError("Request Timeout", "ENETUNREACH", 408);
+    const mockHttpClient = new MockAuthHttpClient({
+      authResponse: [{ status: 200 }, { error: netError }]
+    });
+
+    const credential = new ManagedIdentityCredential(process.env.AZURE_CLIENT_ID, {
+      ...mockHttpClient.tokenCredentialOptions
+    });
+    await assertRejects(
+      credential.getToken("scopes"),
+      (error: AuthenticationError) => error.message.indexOf("Network unreachable.") > -1
+    );
+  });
+
+  it("returns expected error when the host was unreachable", async function() {
+    process.env.AZURE_CLIENT_ID = "errclient";
+
+    const hostError: RestError = new RestError("Request Timeout", "EHOSTUNREACH", 408);
+    const mockHttpClient = new MockAuthHttpClient({
+      authResponse: [{ status: 200 }, { error: hostError }]
     });
 
     const credential = new ManagedIdentityCredential(process.env.AZURE_CLIENT_ID, {
@@ -101,7 +152,7 @@ describe("ManagedIdentityCredential", function() {
     await assertRejects(
       credential.getToken("scopes"),
       (error: AuthenticationError) =>
-        error.errorResponse.error.indexOf("ManagedIdentityCredential authentication failed.") > -1
+        error.message.indexOf("No managed identity endpoint found.") > -1
     );
   });