Merge pull request Azure#9892 from erich-wang/fix-user-msi2

fix userId in system managed identity test cases

Author: cormacpayne

src/Accounts/Authentication.Test/AuthenticationFactoryTests.cs

@@ -365,9 +365,11 @@ public void AppServiceManagedIdentity()
         {
             AzureSessionInitializer.InitializeAzureSession();
             var tenant = Guid.NewGuid().ToString();
+            var userId = "MSI@2";
             var environment = AzureEnvironment.PublicEnvironments["AzureCloud"];
             var account = new AzureAccount
             {
+                Id = userId,
                 Type = AzureAccount.AccountType.ManagedService
             };
             const string resource = @"https://management.azure.com/";
@@ -445,9 +447,11 @@ public void AppServiceManagedIdentityWithDataPlane()
         {
             AzureSessionInitializer.InitializeAzureSession();
             var tenant = Guid.NewGuid().ToString();
+            var userId = "MSI@2";
             var environment = AzureEnvironment.PublicEnvironments["AzureCloud"];
             var account = new AzureAccount
             {
+                Id = userId,
                 Type = AzureAccount.AccountType.ManagedService
             };
             const string resource = @"https://vault.azure.com/";
@@ -484,9 +488,11 @@ public void AppServiceManagedIdentityWithServiceManagement()
         {
             AzureSessionInitializer.InitializeAzureSession();
             var tenant = Guid.NewGuid().ToString();
+            var userId = "MSI@2";
             var environment = AzureEnvironment.PublicEnvironments["AzureCloud"];
             var account = new AzureAccount
             {
+                Id = userId,
                 Type = AzureAccount.AccountType.ManagedService
             };
             const string resource = @"https://management.azure.com/";

src/Accounts/Authentication/Authentication/ManagedServiceAccessTokenBase.cs

@@ -34,7 +34,7 @@ public abstract class ManagedServiceAccessTokenBase<TManagedServiceTokenInfo> :
 
         protected ManagedServiceAccessTokenBase(IAzureAccount account, IAzureEnvironment environment, string resourceId, string tenant = "Common")
         {
-            if (!account.IsPropertySet(AzureAccount.Property.MSILoginUri))
+            if (string.IsNullOrWhiteSpace(account?.Id) || !account.IsPropertySet(AzureAccount.Property.MSILoginUri))
             {
                 throw new ArgumentNullException(nameof(account));
             }