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Securing Your ASP.NET SignalR Hub: Simple Strategies for Robust Protection

Updated: Jun 20

SignalR is a powerful ASP.NET library that enables interactive communication between server and client in real-time web applications. However, with great power comes great responsibility, especially security. This article will explore essential techniques to fortify your SignalR hubs against potential threats. These strategies will help you ensure real-time applications are dynamic, responsive, secure, and trustworthy.

So let’s begin SignalR security and learn how to safeguard your hubs effectively.

Method 1: Apply the [Authorize] attribute to your SignalR hub class

Applying the [Authorize] attribute to your SignalR hub class is a security measure that ensures only authenticated users can access the hub and its methods.

The [Authorize] attribute is an ASP.NET Core attribute used to enforce security policies on controllers, actions, or SignalR hubs. When applied to a SignalR hub class, it specifies that all methods within that hub require the user to be authenticated.

How It Secures SignalR:

  1. Authentication Enforcement: The [Authorize] attribute ensures that an authenticated user creates a connection to the hub. If a user is not authenticated, the connection will be denied.

  2. Global Application: By applying it at the class level, you enforce this policy across all methods within the hub without having to apply it individually to each method.

Here’s how it helps secure your SignalR hub:

using Microsoft.AspNetCore.SignalR;
using Microsoft.AspNetCore.Authorization;

public class ChatHub : Hub
    // Hub methods go here

Authentication Check: When a client attempts to connect to the hub, the [Authorize] attribute triggers an authentication check. If the user is not authenticated, the connection is rejected.

Accessing User Identity: Once a user is authenticated, their identity (User property) is available within the hub context. This allows you to access user information and perform further authorization checks.

public async Task SendMessage(string message)
    var userName = Context.User.Identity.Name;
    await Clients.All.SendAsync("ReceiveMessage", userName, message);

Role-Based Authorization: You can restrict access by specifying roles within the [Authorize] attribute. Ensuring only users with the specified roles can access the hub methods.

[Authorize(Roles = "Admin")]
public class AdminHub : Hub
    public async Task SendAdminMessage(string message)
        await Clients.All.SendAsync("ReceiveAdminMessage", message);

Policy-Based Authorization: You can also use policies for more complex authorization scenarios. Policies are configured in the Startup.cs file and then applied using the [Authorize] attribute.

// In Startup.cs
services.AddAuthorization(options =>
    options.AddPolicy("MustBeAdmin", policy => policy.RequireRole("Admin"));

// In your Hub class
[Authorize(Policy = "MustBeAdmin")]
public class AdminHub : Hub
    // Hub methods for admins

Apply these authorization checks to ensure that only authenticated and authorized users can access your SignalR hub, which helps protect against unauthorized access and potential security threats.

Method 2: Set up the HubConnection with an access token

HubConnection is an ASP.NET Core SignalR library class representing a connection between the client and the server hub. It’s responsible for managing the connection, sending messages to the server hub, and receiving messages from it.

Securing a HubConnection is essential to prevent several potential risks:

  1. Malicious actors could intercept the data transmitted between the client and server, leading to data breaches.

  2. Unsecured connections are vulnerable to tampering, where an attacker could alter messages in transit.

  3. If connections are not authenticated, attackers could impersonate legitimate users and gain unauthorized access to the system.

  4. Secure connections help protect against attacks that aim to disrupt service, such as flooding a hub with unauthorized connection requests.

If a HubConnection is not secured, it could lead to:

  • Data Theft: Sensitive information such as personal details, financial data, or confidential communications could be stolen.

  • Data Corruption: The integrity of the data could be compromised, affecting business processes and decision-making.

  • Unauthorized Actions: Attackers could perform unauthorized actions on behalf of users, which could lead to fraud or other malicious activities.

  • Legal and Compliance Issues: There may be legal consequences for failing to protect user data, including fines and damage to reputation.

Here's how you can secure the SignalR hub with HubConnection:

  1. Injecting Dependencies: Inject IAccessTokenProvider to request access tokens and NavigationManager to resolve URLs.

@using Microsoft.AspNetCore.Components.WebAssembly.Authentication
@inject IAccessTokenProvider TokenProvider
@inject NavigationManager Navigation
  1. Requesting an Access Token: Use the IAccessTokenProvider to request an access token. If the user is authenticated, you’ll receive a token.

var tokenResult = await TokenProvider.RequestAccessToken();

if (tokenResult.TryGetToken(out var token))
    // Proceed to set up the HubConnection with the token
  1. Setting Up HubConnection: Create a new HubConnectionBuilder, configure it with the URL of your SignalR hub, and provide an access token provider function that returns the token you obtained.

hubConnection = new HubConnectionBuilder()
        options => { options.AccessTokenProvider = () => Task.FromResult(token.Value); })
  1. Starting the Connection: Finally, start the connection to establish communication with the SignalR hub.

await hubConnection.StartAsync();


  • Authentication: The access token represents the user’s authenticated session. The SignalR hub will use this token to verify that the user is authenticated.

  • Authorization: If you have role-based or policy-based authorization on the server side, the token will also contain claims about the user’s roles or policies, which SignalR uses to authorize access.

  • Secure Communication: By providing an access token for each connection attempt, you ensure that only users with valid tokens (i.e., authenticated users) can communicate with the hub.

Method 3: Configure CORS

Configuring Cross-Origin Resource Sharing (CORS) is a crucial security measure for web applications, including those using SignalR. It allows you to specify which origins are permitted to make requests to your server, thus preventing unauthorized domains from interacting with your resources.

Follow the below steps to configure CORS:

STEP 1: Defining a CORS Policy:

In the ConfigureServices method of your Startup.cs file, you define a CORS policy using the AddCors method. This policy dictates which origins are allowed to send requests to your server.

services.AddCors(options =>
    options.AddPolicy("CorsPolicy", builder =>
        builder.WithOrigins("") // Replace with your client's domain

STEP 2: Setting Allowed Origins: The WithOrigins method specifies allowed domains. In this case, only is permitted. Replace this with the actual domain of your Blazor client application.

STEP 3: Allowing Headers and Methods: The .AllowAnyHeader() and .AllowAnyMethod() methods indicate that any HTTP headers and methods can be used in the cross-origin requests.

STEP 4: Handling Credentials: The .AllowCredentials() method allows credentials (such as cookies or HTTP authentication) in cross-origin requests.

STEP 5: Applying the CORS Policy: In the Configure method, you apply the defined CORS policy using app.UseCors("CorsPolicy"). This ensures that all incoming HTTP requests are evaluated against the policy.

public void Configure(IApplicationBuilder app, IWebHostEnvironment env)

    // Other configurations...

By configuring CORS this way, you ensure that:

  • Only requests from trusted origins (your Blazor client) can interact with your SignalR hub.

  • You prevent potentially malicious websites from using your SignalR hub, which could lead to cross-site scripting (XSS) attacks or data leaks.

  • Your SignalR hub is only accessible by authenticated users from the allowed origin.

Method 4: Require Authentication Globally

In securing SignalR hubs, RequireAuthentication enforces a user must be authenticated to access a particular hub. When you call RequireAuthentication during your application’s endpoints, the ASP.NET Core framework should not allow anonymous users to connect to the hub. This method is part of the authorization middleware that checks if a valid authentication token is associated with the request. If there isn’t, the request is rejected, and the user cannot establish a connection to the hub.

By using RequireAuthentication, you ensure that all communication through the SignalR hub is performed by users authenticated by your application’s security system, thus protecting your application from unauthorized access.

To use RequireAuthentication for securing your SignalR hubs, follow these steps:

STEP 1: Configure Authentication:

First, ensure that authentication is properly configured in your application. This typically involves setting up an identity provider and configuring the authentication middleware in the Startup.cs file.

public void ConfigureServices(IServiceCollection services)
    // Add authentication services
    services.AddAuthentication(/* ... */);

    // Other services...

STEP 2: Apply Authentication Middleware:

In the Configure method, apply the authentication middleware using app.UseAuthentication() before the call to app.UseEndpoints.

public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
    // Other configurations...


    // Other configurations...

STEP 3: Map Hubs and Require Authentication:

Within the app.UseEndpoints configuration, map each SignalR hub to a route, and chain the RequireAuthorization() method to enforce authentication.

app.UseEndpoints(endpoints =>
    // Map other hubs and require authorization as needed

STEP 4: Test the Configuration:

Test your application to ensure that only authenticated users can access the hubs. You can do this by attempting to connect to the hub without providing authentication credentials and verifying that the connection is rejected.

Method 5: Role-Based Authorization

Role-based authorization in SignalR allows you to restrict access to certain hubs or hub methods based on the roles assigned to a user.

The [Authorize(Roles = "role")] attribute in ASP.NET Core is used to implement role-based authorization. It specifies that access to a particular resource, such as a controller, action method, or SignalR hub, is restricted to users assigned a specific role or roles.

[Authorize(Roles = "role")]
  1. Attribute Usage: The [Authorize] attribute can be placed above a class or method. When used with the Roles property, like [Authorize(Roles = "Admin")], it restricts access to users who are authenticated and assigned the “Admin” role.

  2. Multiple Roles: You can specify multiple roles by separating them with commas, like [Authorize(Roles = "Admin, Manager")]. This allows users who have any of the listed roles.

  3. Role Checks: When a request is made to an action or hub protected by this attribute, the framework checks the roles associated with the user’s identity against the specified attribute.

  4. Authorization Failure: If the user does not have the required role, the framework returns an HTTP 403 Forbidden status code, denying access to the resource.

  5. Combinational Use: The [Authorize] attribute can be combined with other attributes for more complex authorization scenarios, such as policy-based authorization.

Using the [Authorize(Roles = "role")] attribute is a straightforward way to enforce role-based access control in your ASP.NET Core applications.

Here’s how to use the [Authorize(Roles = "role")] attribute:

  1. Role Definition: Roles are typically defined in your identity system (e.g., ASP.NET Core Identity) and are assigned to users to represent their permissions within the application.

  2. Authorize Attribute: The [Authorize] attribute is an ASP.NET Core feature that can be applied to controllers, actions, or SignalR hubs and methods to enforce security policies.

  3. Specifying Roles: By specifying Roles = "role" within the [Authorize] attribute, you’re indicating that only users with the specified role(s) are allowed access. For example, [Authorize(Roles = "Admin")] means only users with the “Admin” role can access the hub or method.

[Authorize(Roles = "Admin")]
public class AdminHub : Hub
    // Hub methods for admins
  1. Applying to Hubs: When you apply this attribute to a SignalR hub class, like AdminHub, it enforces that all methods within that hub can only be accessed by users who have been authenticated and have the specified role.

  2. Granular Access Control: You can also apply the [Authorize] attribute to individual hub methods for more granular access control, allowing different roles for different methods within the same hub.

  3. Security Enforcement: When a user attempts to connect to a hub or invoke a method with role-based authorization, the SignalR framework checks if the user’s identity includes the required role. If not, access is denied.

Method 6: Use SSL/TLS

SSL/TLS are protocols that encrypt data transmitted over the internet, ensuring that any data sent between the client and server is unreadable to anyone who might intercept it. This is particularly important for real-time web applications like those using SignalR, where sensitive information may be transmitted.

How SSL/TLS Secures SignalR:

  1. Encryption: SSL/TLS encrypts the data being sent back and forth between the client and server, which prevents potential eavesdroppers from understanding the data.

  2. Authentication: The server presents a certificate to prove its identity to the client. Clients can be configured to require a certificate for mutual authentication.

  3. Data Integrity: SSL/TLS ensures that the data has not been tampered with during transit.

How to Use SSL/TLS with SignalR:

  1. Obtain an SSL/TLS Certificate: You can purchase a certificate from a trusted Certificate Authority (CA) or obtain one from a free provider like Let’s Encrypt.

  2. Install the Certificate on Your Server: Follow your hosting provider’s instructions to install the certificate on your server.

  3. Configure Your Application to Use HTTPS: In your ASP.NET Core application’s Startup.cs file, ensure you have the following middleware:

public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
    app.UseHttpsRedirection(); // Redirects HTTP requests to HTTPS
    // Other configurations...
  1. Ensure SignalR Clients Use WSS (WebSocket Secure): When connecting to your SignalR hub, clients should use the wss:// protocol instead of ws://. For example:

const connection = new signalR.HubConnectionBuilder()
  1. Enforce HTTPS in Production: Ensure your production environment is configured to only serve content over HTTPS.


As we wrap up our exploration of securing ASP.NET SignalR hubs, it’s clear that implementing robust security measures is not just a recommendation—it’s a necessity. Applying the strategies discussed, from authentication checks with the [Authorize] attribute to role and policy-based authorization, you can create a secure environment for your real-time applications.


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