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: 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. csharp 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. csharp [Authorize(AuthenticationSchemes = "CustomScheme")] public IActionResult SecureAction() { // This action is protected by your custom authentication scheme return View(); } You can also enforce authentication programmatically in your code: csharp 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: csharp public void Configure(IApplicationBuilder app, IWebHostEnvironment env) { // Other middleware configurations... app.UseAuthentication(); app.UseAuthorization(); // More middleware configurations... } Now, you have a basic custom authentication scheme in place. Customize the CustomAuthenticationHandler to fit your specific authentication logic, such as validating user credentials, creating a ClaimsPrincipal, and issuing authentication tickets. Additionally, you can add more advanced features, such as handling authentication challenges and events. read less