SignalR: Configuring CORS

Introduction

This tutorial covers the configuration of Cross-Origin Resource Sharing (CORS) for SignalR. CORS is essential when your SignalR hub and clients are hosted on different domains, allowing you to control which domains are permitted to access your SignalR resources.

Configuring CORS for SignalR

Syntax

Configuring CORS for SignalR involves modifying the SignalR hub configuration on the server side to specify allowed origins. The basic syntax is as follows:

public void ConfigureServices(IServiceCollection services)
{
    services.AddCors(options =>
    {
        options.AddPolicy("CorsPolicy",
            builder => builder
                .WithOrigins("http://alloweddomain1.com", "https://alloweddomain2.com")
                .AllowAnyMethod()
                .AllowAnyHeader()
                .AllowCredentials());
    });

    services.AddSignalR();
}

Example

Consider a scenario where your SignalR server is hosted at http://signalr-server.com and you want to allow connections from http://client-domain.com.

public void ConfigureServices(IServiceCollection services)
{
    services.AddCors(options =>
    {
        options.AddPolicy("CorsPolicy",
            builder => builder
                .WithOrigins("http://client-domain.com")
                .AllowAnyMethod()
                .AllowAnyHeader()
                .AllowCredentials());
    });

    services.AddSignalR();
}

Explanation

• AddCors Method: Configures the CORS middleware for the application.
• .WithOrigins: Specifies the allowed origins (domains) that can access the SignalR resources.
• .AllowAnyMethod: Allows any HTTP method (GET, POST, etc.).
• .AllowAnyHeader: Allows any HTTP headers in the request.
• .AllowCredentials: Allows the use of credentials (e.g., cookies) when making requests.

Use

• Cross-Domain SignalR: Enable SignalR communication between applications hosted on different domains.
• Secure Communication: Control which domains can access your SignalR resources to enhance security.
• Third-Party Integrations: Facilitate integration with third-party applications or services.

Important Points

1. CORS configuration must be done on the server side where the SignalR hub is hosted.
2. Ensure that you specify the correct allowed origins to prevent unauthorized access.
3. Be mindful of security implications, especially when using the .AllowAnyOrigin() method.

Summary

Configuring CORS for SignalR is crucial when building applications that involve cross-origin communication. By specifying allowed origins, you control which domains can connect to your SignalR hub, ensuring secure and controlled access to real-time communication features.