Custom authentication in asp net core

Introduction

Custom authentication is a common requirement in ASP.NET Core applications. While ASP.NET Core provides built-in authentication mechanisms, there are scenarios you may need to implement your own custom authentication . In this article, we will explore how to implement custom authentication in ASP.NET Core with .

Prerequisites

Before we dive into the implementation, make sure you have the following prerequisites:

  • Basic understanding of ASP.NET Core
  • Visual Studio or any other code

Step 1: Create a new ASP.NET Core project

First, let's create a new ASP.NET Core project. Open Visual Studio and follow these steps:

  1. Select “Create a new project” from the start page.
  2. Choose “ASP.NET Core Web Application” template.
  3. Provide a name and location for your project.
  4. Select “Web Application” as the project template.
  5. Click “Create” to create the project.

Step 2: Implement custom authentication logic

Now, let's implement the custom authentication logic in our ASP.NET Core application. Open the “.cs” file and add the following code inside the “ConfigureServices” :


services.AddAuthentication(options =>
{
    options.DefaultAuthenticateScheme = "CustomScheme";
    options.DefaultChallengeScheme = "CustomScheme";
})
.AddScheme("CustomScheme", options => { });

In the above code, we are configuring the authentication services to use a custom authentication scheme “CustomScheme”. We also specify the default authentication and challenge schemes as “CustomScheme”.

Next, let's create the custom authentication options and handler. Add the following code to a new file called “CustomAuthenticationOptions.cs”:


public class CustomAuthenticationOptions : AuthenticationSchemeOptions
{
    public string CustomClaimType { get; set; }
}

In the above code, we define a custom authentication options class that inherits from the base “AuthenticationSchemeOptions” class. We also add a property called “CustomClaimType” to store the custom claim type.

Now, let's create the custom authentication handler. Add the following code to a new file called “CustomAuthenticationHandler.cs”:


public class CustomAuthenticationHandler : AuthenticationHandler
{
    public CustomAuthenticationHandler(IOptionsMonitor options, ILoggerFactory logger, UrlEncoder encoder, ISystemClock ) : base(options, logger, encoder, clock)
    {
    }

    protected override async Task HandleAuthenticateAsync()
    {
        // Custom authentication logic goes here
        // Retrieve the authentication token from the request
        // Validate the token and extract the necessary claims
        // Create a ClaimsPrincipal object and set it as the User property

        var claims = new List
        {
            new Claim(Options.CustomClaimType, "CustomClaimValue")
        };

        var  = new (claims, Scheme.Name);
        var principal = new ClaimsPrincipal(identity);
        var ticket = new AuthenticationTicket(principal, Scheme.Name);

        return await Task.FromResult(AuthenticateResult.Success(ticket));
    }
}

In the above code, we create a custom authentication handler by inheriting from the base “AuthenticationHandler” class. We override the “HandleAuthenticateAsync” method to implement our custom authentication logic. Inside this method, we can retrieve the authentication token from the request, validate it, and create a ClaimsPrincipal object with the necessary claims.

Step 3: Use custom authentication in controllers

Now that we have implemented the custom authentication logic, let's use it in our controllers. Open a controller file and add the following code to the desired action method:


[Authorize(AuthenticationSchemes = "CustomScheme")]
public IActionResult CustomAuthenticatedAction()
{
    // Custom authenticated action logic goes here
    return View();
}

In the above code, we use the “Authorize” attribute to specify that the action method requires authentication using the “CustomScheme”. This ensures that only authenticated users with the custom authentication scheme can access the action method.

Conclusion

In this article, we have explored how to implement custom authentication in ASP.NET Core. We have seen how to configure the authentication services, create custom authentication options and handler, and use custom authentication in controllers. By following these steps, you can easily implement your own custom authentication logic in ASP.NET Core applications.

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