How can I create and use custom authentication in ASP.NET Core?

Creating and using custom authentication in ASP.NET Core involves implementing your own authentication scheme. Here's a basic guide on how to create a custom authentication scheme in ASP.NET Core:

1. Create a Custom Authentication Handler:

   Start by creating a custom authentication handler by inheriting from the AuthenticationHandler<TOptions> class. This class provides the basic infrastructure for handling authentication.

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• public class CustomAuthenticationHandler : AuthenticationHandler<CustomAuthenticationOptions> { public CustomAuthenticationHandler(IOptionsMonitor<CustomAuthenticationOptions> options, ILoggerFactory logger, UrlEncoder encoder, ISystemClock clock) : base(options, logger, encoder, clock) { } protected override async Task<AuthenticateResult> HandleAuthenticateAsync() { // Implement your authentication logic here // Retrieve credentials from the request, validate them, and create a ClaimsPrincipal // Example: var claims = new List<Claim> { new Claim(ClaimTypes.Name, "JohnDoe"), // Add other claims as needed }; var identity = new ClaimsIdentity(claims, Scheme.Name); var principal = new ClaimsPrincipal(identity); var ticket = new AuthenticationTicket(principal, Scheme.Name); return AuthenticateResult.Success(ticket); } }

• Create Custom Authentication Options:

  Define a class for custom authentication options by inheriting from AuthenticationSchemeOptions. This class can contain any configuration properties needed for your authentication scheme.

  csharp
• public class CustomAuthenticationOptions : AuthenticationSchemeOptions { // Add any custom properties/configuration needed for your authentication scheme }

• Register Custom Authentication in Startup.cs:

  In the Startup.cs file, add the custom authentication scheme during the ConfigureServices method:

  csharp
• public void ConfigureServices(IServiceCollection services) { // Other service configurations... services.AddAuthentication(CustomAuthenticationOptions.DefaultScheme) .AddScheme<CustomAuthenticationOptions, CustomAuthenticationHandler>("CustomScheme", options => { /* configure options if needed */ }); // More service configurations... }

• Use Custom Authentication in Controllers:

  In your controllers or action methods, use the Authorize attribute with your custom authentication scheme name.

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You can also enforce authentication programmatically in your code:

• var result = await HttpContext.AuthenticateAsync("CustomScheme"); if (!result.Succeeded) { // Handle authentication failure return Challenge("CustomScheme"); } // Continue processing for authenticated user

• Configure Authentication Middleware:

  In the Configure method of Startup.cs, add the authentication middleware to the request processing pipeline:

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