Change Azure authentication order

Based on recommendations from Microsoft, change the order valid
authentication options are taken into account. Mainly to ensure it works
as expected when multiple Managed Identities are bound on the same VM
node.

Signed-off-by: Hidde Beydals <hello@hidde.co>

Author: hiddeco

pkg/azure/blob.go

@@ -63,15 +63,15 @@ type BlobClient struct {
 // Bucket and Secret. It detects credentials in the Secret in the following
 // order:
 //
-//  - azidentity.ManagedIdentityCredential for a Resource ID, when a
-//   `resourceId` field is found.
-//  - azidentity.ManagedIdentityCredential for a User ID, when a `clientId`
-//    field but no `tenantId` is found.
+//  - azidentity.ClientSecretCredential when `tenantId`, `clientId` and
+//    `clientSecret` fields are found.
 //  - azidentity.ClientCertificateCredential when `tenantId`,
 //    `clientCertificate` (and optionally `clientCertificatePassword`) fields
 //    are found.
-//  - azidentity.ClientSecretCredential when `tenantId`, `clientId` and
-//    `clientSecret` fields are found.
+//  - azidentity.ManagedIdentityCredential for a User ID, when a `clientId`
+//    field but no `tenantId` is found.
+//  - azidentity.ManagedIdentityCredential for a Resource ID, when a
+//   `resourceId` field is found.
 //	- azblob.SharedKeyCredential when an `accountKey` field is found.
 //    The account name is extracted from the endpoint specified on the Bucket
 //    object.
@@ -271,31 +271,30 @@ func (c *BlobClient) ObjectIsNotFound(err error) bool {
 }
 
 func tokenCredentialFromSecret(secret *corev1.Secret) (azcore.TokenCredential, error) {
-	var token azcore.TokenCredential
-	if resourceID, ok := secret.Data[resourceIDField]; ok {
-		return azidentity.NewManagedIdentityCredential(&azidentity.ManagedIdentityCredentialOptions{
-			ID: azidentity.ResourceID(resourceID),
-		})
-	}
-	if clientID, hasClientID := secret.Data[clientIDField]; hasClientID {
-		tenantID, hasTenantID := secret.Data[tenantIDField]
-		if !hasTenantID {
-			return azidentity.NewManagedIdentityCredential(&azidentity.ManagedIdentityCredentialOptions{
-				ID: azidentity.ClientID(clientID),
-			})
+	clientID, hasClientID := secret.Data[clientIDField]
+	if tenantID, hasTenantID := secret.Data[tenantIDField]; hasTenantID && hasClientID {
+		if clientSecret, hasClientSecret := secret.Data[clientSecretField]; hasClientSecret && len(clientSecret) > 0 {
+			return azidentity.NewClientSecretCredential(string(tenantID), string(clientID), string(clientSecret), nil)
 		}
-		if clientCertificate, hasClientCertificate := secret.Data[clientCertificateField]; hasClientCertificate {
+		if clientCertificate, hasClientCertificate := secret.Data[clientCertificateField]; hasClientCertificate && len(clientCertificate) > 0 {
 			certs, key, err := azidentity.ParseCertificates(clientCertificate, secret.Data[clientCertificatePasswordField])
 			if err != nil {
 				return nil, fmt.Errorf("failed to parse client certificates: %w", err)
 			}
 			return azidentity.NewClientCertificateCredential(string(tenantID), string(clientID), certs, key, nil)
 		}
-		if clientSecret, hasClientSecret := secret.Data[clientSecretField]; hasClientSecret {
-			return azidentity.NewClientSecretCredential(string(tenantID), string(clientID), string(clientSecret), nil)
-		}
 	}
-	return token, nil
+	if hasClientID {
+		return azidentity.NewManagedIdentityCredential(&azidentity.ManagedIdentityCredentialOptions{
+			ID: azidentity.ClientID(clientID),
+		})
+	}
+	if resourceID, hasResourceID := secret.Data[resourceIDField]; hasResourceID {
+		return azidentity.NewManagedIdentityCredential(&azidentity.ManagedIdentityCredentialOptions{
+			ID: azidentity.ResourceID(resourceID),
+		})
+	}
+	return nil, nil
 }
 
 func sharedCredentialFromSecret(endpoint string, secret *corev1.Secret) (*azblob.SharedKeyCredential, error) {