use MSI_ENDPOINT when required for availability

autorest/adal/token.go

@@ -1317,12 +1317,28 @@ func NewMultiTenantServicePrincipalTokenFromCertificate(multiTenantCfg MultiTena
 
 // MSIAvailable returns true if the MSI endpoint is available for authentication.
 func MSIAvailable(ctx context.Context, s Sender) bool {
+	_, _, err := getMSIAvailable(ctx, s)
+	return err == nil
+}
+
+// getMSIAvailable returns the response from the resolved MSI endpoint, the MSI endpoint used, and the error returned
+func getMSIAvailable(ctx context.Context, s Sender) (*http.Response, string, error) {
 	if s == nil {
 		s = sender()
 	}
-	resp, err := getMSIEndpoint(ctx, s)
+	msiType, endpoint, err := getMSIType()
+	if err != nil {
+		return nil, endpoint, err
+	}
+
+	var apiVersion string
+	if apiVersion = msiAPIVersion; msiType == msiTypeAppServiceV20170901 {
+		apiVersion = appServiceAPIVersion2017
+	}
+
+	resp, err := getMSIEndpoint(ctx, s, endpoint, apiVersion)
 	if err == nil {
 		resp.Body.Close()
 	}
-	return err == nil
+	return resp, endpoint, err
 }

autorest/adal/token_1.13.go

@@ -24,13 +24,13 @@ import (
 	"time"
 )
 
-func getMSIEndpoint(ctx context.Context, sender Sender) (*http.Response, error) {
+func getMSIEndpoint(ctx context.Context, sender Sender, endpoint string, apiVersion string) (*http.Response, error) {
 	tempCtx, cancel := context.WithTimeout(ctx, 2*time.Second)
 	defer cancel()
 	// http.NewRequestWithContext() was added in Go 1.13
-	req, _ := http.NewRequestWithContext(tempCtx, http.MethodGet, msiEndpoint, nil)
+	req, _ := http.NewRequestWithContext(tempCtx, http.MethodGet, endpoint, nil)
 	q := req.URL.Query()
-	q.Add("api-version", msiAPIVersion)
+	q.Add("api-version", apiVersion)
 	req.URL.RawQuery = q.Encode()
 	return sender.Do(req)
 }

autorest/adal/token_test.go

@@ -1343,6 +1343,40 @@ func TestMSIAvailableSuccess(t *testing.T) {
 	}
 }
 
+func TestMSIAvailableAppService(t *testing.T) {
+	os.Setenv("MSI_ENDPOINT", "http://localhost")
+	os.Setenv("MSI_SECRET", "super")
+	defer func() {
+		os.Unsetenv("MSI_ENDPOINT")
+		os.Unsetenv("MSI_SECRET")
+	}()
+	c := mocks.NewSender()
+	c.AppendResponse(mocks.NewResponse())
+	_, endpoint, err := getMSIAvailable(context.Background(), c)
+
+	if err != nil {
+		t.Fatal("unexpected error")
+	}
+
+	if endpoint != "http://localhost" {
+		t.Fatal("incorrect endpoint returned")
+	}
+}
+
+func TestMSIAvailableIMDS(t *testing.T) {
+	c := mocks.NewSender()
+	c.AppendResponse(mocks.NewResponse())
+	_, endpoint, err := getMSIAvailable(context.Background(), c)
+
+	if err != nil {
+		t.Fatal("unexpected error")
+	}
+
+	if endpoint != msiEndpoint {
+		t.Fatal("incorrect endpoint returned")
+	}
+}
+
 func TestMSIAvailableSlow(t *testing.T) {
 	c := mocks.NewSender()
 	// introduce a long response delay to simulate the endpoint not being available
@@ -1359,7 +1393,7 @@ func TestMSIAvailableFail(t *testing.T) {
 	if MSIAvailable(context.Background(), c) {
 		t.Fatal("unexpected true")
 	}
-	_, err := getMSIEndpoint(context.Background(), c)
+	_, err := getMSIEndpoint(context.Background(), c, msiEndpoint, msiAPIVersion)
 	if !strings.Contains(err.Error(), "") {
 		t.Fatalf("expected error: '%s', but got error '%s'", expectErr, err)
 	}