Link from SignalR groups to authn/authz (#18354)

Author: serpent5

aspnetcore/signalr/groups.md

@@ -5,7 +5,7 @@ description: Overview of ASP.NET Core SignalR User and Group management.
 monikerRange: '>= aspnetcore-2.1'
 ms.author: bradyg
 ms.custom: mvc
-ms.date: 11/12/2019
+ms.date: 05/17/2020
 no-loc: [Blazor, "Identity", "Let's Encrypt", Razor, SignalR]
 uid: signalr/groups
 ---
@@ -20,24 +20,26 @@ SignalR allows messages to be sent to all connections associated with a specific
 
 ## Users in SignalR
 
-SignalR allows you to send messages to all connections associated with a specific user. By default, SignalR uses the `ClaimTypes.NameIdentifier` from the `ClaimsPrincipal` associated with the connection as the user identifier. A single user can have multiple connections to a SignalR app. For example, a user could be connected on their desktop as well as their phone. Each device has a separate SignalR connection, but they're all associated with the same user. If a message is sent to the user, all of the connections associated with that user receive the message. The user identifier for a connection can be accessed by the `Context.UserIdentifier` property in your hub.
+A single user in SignalR can have multiple connections to an app. For example, a user could be connected on their desktop as well as their phone. Each device has a separate SignalR connection, but they're all associated with the same user. If a message is sent to the user, all of the connections associated with that user receive the message. The user identifier for a connection can be accessed by the `Context.UserIdentifier` property in the hub.
 
-Send a message to a specific user by passing the user identifier to the `User` function in your hub method as shown in the following example:
+By default, SignalR uses the `ClaimTypes.NameIdentifier` from the `ClaimsPrincipal` associated with the connection as the user identifier. To customize this behavior, see [Use claims to customize identity handling](xref:signalr/authn-and-authz#use-claims-to-customize-identity-handling).
+
+Send a message to a specific user by passing the user identifier to the `User` function in a hub method, as shown in the following example:
 
 > [!NOTE]
 > The user identifier is case-sensitive.
 
-[!code-csharp[Configure service](groups/sample/hubs/chathub.cs?range=29-32)]
+[!code-csharp[Configure service](groups/sample/Hubs/ChatHub.cs?range=29-32)]
 
 ## Groups in SignalR
 
-A group is a collection of connections associated with a name. Messages can be sent to all connections in a group. Groups are the recommended way to send to a connection or multiple connections because the groups are managed by the application. A connection can be a member of multiple groups. This makes groups ideal for something like a chat application, where each room can be represented as a group. Connections can be added to or removed from groups via the `AddToGroupAsync` and `RemoveFromGroupAsync` methods.
+A group is a collection of connections associated with a name. Messages can be sent to all connections in a group. Groups are the recommended way to send to a connection or multiple connections because the groups are managed by the application. A connection can be a member of multiple groups. Groups are ideal for something like a chat application, where each room can be represented as a group. Connections are added to or removed from groups via the `AddToGroupAsync` and `RemoveFromGroupAsync` methods.
 
-[!code-csharp[Hub methods](groups/sample/hubs/chathub.cs?range=15-27)]
+[!code-csharp[Hub methods](groups/sample/Hubs/ChatHub.cs?range=15-27)]
 
 Group membership isn't preserved when a connection reconnects. The connection needs to rejoin the group when it's re-established. It's not possible to count the members of a group, since this information is not available if the application is scaled to multiple servers.
 
-To protect access to resources while using groups, use [authentication and authorization](xref:signalr/authn-and-authz) functionality in ASP.NET Core. If you only add users to a group when the credentials are valid for that group, messages sent to that group will only go to authorized users. However, groups are not a security feature. Authentication claims have features that groups do not, such as expiry and revocation. If a user's permission to access the group is revoked, you have to manually detect that and remove them from the group.
+To protect access to resources while using groups, use [authentication and authorization](xref:signalr/authn-and-authz) functionality in ASP.NET Core. If a user is added to a group only when the credentials are valid for that group, messages sent to that group will only go to authorized users. However, groups are not a security feature. Authentication claims have features that groups do not, such as expiry and revocation. If a user's permission to access the group is revoked, the app must remove the user from the group explicitly.
 
 > [!NOTE]
 > Group names are case-sensitive.