49 lines
3.2 KiB
Markdown
49 lines
3.2 KiB
Markdown
---
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title: Manage users and groups in SignalR
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author: bradygaster
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description: Overview of ASP.NET Core SignalR User and Group management.
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monikerRange: '>= aspnetcore-2.1'
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ms.author: bradyg
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ms.custom: mvc
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ms.date: 06/04/2018
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uid: signalr/groups
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---
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# Manage users and groups in SignalR
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By [Brennan Conroy](https://github.com/BrennanConroy)
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SignalR allows messages to be sent to all connections associated with a specific user, as well as to named groups of connections.
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[View or download sample code](https://github.com/aspnet/AspNetCore.Docs/tree/master/aspnetcore/signalr/groups/sample/) [(how to download)](xref:index#how-to-download-a-sample)
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## Users in SignalR
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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.
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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:
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> [!NOTE]
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> The user identifier is case-sensitive.
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[!code-csharp[Configure service](groups/sample/hubs/chathub.cs?range=29-32)]
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## Groups in SignalR
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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.
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[!code-csharp[Hub methods](groups/sample/hubs/chathub.cs?range=15-27)]
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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.
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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.
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> [!NOTE]
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> Group names are case-sensitive.
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## Related resources
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* [Get started](xref:tutorials/signalr)
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* [Hubs](xref:signalr/hubs)
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* [Publish to Azure](xref:signalr/publish-to-azure-web-app)
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