add AADSTS50020 to troubleshooting doc (Azure#37786)

Author: christothes

sdk/identity/Azure.Identity/TROUBLESHOOTING.md

@@ -239,6 +239,7 @@ curl 'http://169.254.169.254/metadata/identity/oauth2/token?resource=https://man
 |Failed To Read VS Code Credentials</p></p>OR</p>Authenticate via Azure Tools plugin in VS Code|No Azure account information was found in the VS Code configuration.|<ul><li>Ensure the [Azure Account plugin](https://marketplace.visualstudio.com/items?itemName=ms-vscode.azure-account) is properly installed</li><li>Use **View > Command Palette** to execute the **Azure: Sign In** command. This command opens a browser window and displays a page that allows you to sign in to Azure.</li><li>If you already had the Azure Account extension installed and logged in to your account, try logging out and logging in again. Doing so will repopulate the cache and potentially mitigate the error you're getting.</li></ul>|
 |MSAL Interaction Required Error|The `VisualStudioCodeCredential` was able to read the cached credentials from the cache but the cached token is likely expired.|Log into the Azure Account extension via **View > Command Palette** to execute the **Azure: Sign In** command in the VS Code IDE.|
 |ADFS tenant not supported|ADFS tenants aren't currently supported by Visual Studio `Azure Service Authentication`.|Use credentials from a supported cloud when authenticating with Visual Studio. The supported clouds are:</p><ul><li>AZURE PUBLIC CLOUD - https://login.microsoftonline.com/</li><li>AZURE GERMANY - https://login.microsoftonline.de/</li><li>AZURE CHINA - https://login.chinacloudapi.cn/</li><li>AZURE GOVERNMENT - https://login.microsoftonline.us/</li></ul>|
+|AADSTS50020| User account '{EmailHidden}' from identity provider 'live.com' doesn't exist in tenant 'Microsoft Services' and cannot access the application '04f0c124-f2bc-4f59-8241-bf6df9866bbd'(VS with native MSA) in that tenant. The account needs to be added as an external user in the tenant first. Sign out and sign in again with a different Azure Active Directory user account.|Specify a `TenantId` value that corresponds to the resource to which you're authenticating in the `VisualStudioCredentialOptions` (or the `DefaultAzureCredentialOptions` if you're using `DefaultAzureCredential`).|
 
 ## Troubleshoot `VisualStudioCredential` authentication issues
 

sdk/identity/Azure.Identity/src/Credentials/ManagedIdentityCredential.cs

@@ -10,8 +10,8 @@
 namespace Azure.Identity
 {
     /// <summary>
-    /// Attempts authentication using a managed identity that has been assigned to the deployment environment. This authentication type works in Azure VMs,
-    /// App Service and Azure Functions applications, as well as the Azure Cloud Shell. More information about configuring managed identities can be found here:
+    /// Attempts authentication using a managed identity that has been assigned to the deployment environment. This authentication type works for all Azure hosted
+    /// environments that support managed identity. More information about configuring managed identities can be found here:
     /// https://docs.microsoft.com/azure/active-directory/managed-identities-azure-resources/overview
     /// </summary>
     public class ManagedIdentityCredential : TokenCredential