Included documentation about "Sharing the same Token Cache database between apps"

Author: Tiago Brenck

2-WebApp-graph-user/2-2-TokenCache/README.md

@@ -102,10 +102,19 @@ public void ConfigureServices(IServiceCollection services)
 The aforementioned four lines of code are explained below.
 
 1. The first two lines enable MSAL.NET to hook-up to the OpenID Connect events to redeem the authorization code obtained by the ASP.NET Core middleware. After obtaining a token for Microsoft Graph, it saves it into the token cache, for use by the Controllers.
-1. The last two lines hook up the Sql server database based token caching solution to MSAL.NET. The Sql based token cache requires a **Connection string** named `TokenCacheDbConnStr` available in the **ConnectionStrings** collections of the **appsettings.json** configuration file. 
+1. The last two lines hook up the Sql server database based token caching solution to MSAL.NET. The Sql based token cache requires a **Connection string** named `TokenCacheDbConnStr` available in the **ConnectionStrings** collections of the **appsettings.json** configuration file.
 
 The files `MSALAppSqlTokenCacheProvider.cs` and `MSALPerUserSqlTokenCacheProvider` of the `Microsoft.Identity.Web` project contains the app and per-user token cache implementations that use Sql server as the token cache.
 
+### Sharing the same Token Cache database between apps
+
+Since we are using `IDataProtector` to protect the token being persisted on the database, in order to enable it to be used between different apps, `SetApplicationName()` must be configured with the same value for all apps. You can read [more details about IDataProtector here.](https://docs.microsoft.com/en-us/aspnet/core/security/data-protection/configuration/overview?view=aspnetcore-2.2#setapplicationname)
+
+```csharp
+services.AddDataProtection()
+        .SetApplicationName("WebApp_Tutorial");
+```
+
 ## Next steps
 
 - Learn how to enable distributed caches in [token cache serialization](../2.2.%20token%20cache%20serialization)