Round #716

Implement a JwtBearerOptions handler that validates a custom claim transformation using IClaimsTransformation in DI.

**Custom Claim Transformation using IClaimsTransformation** =========================================================== In this example, we will implement a custom claim transformation using `IClaimsTransformation` and validate it using `JwtBearerOptions` in a .NET Core application. **IClaimsTransformation Implementation** -------------------------------------- First, let's create a custom implementation of `IClaimsTransformation` that adds a custom claim to the principal: ```csharp using Microsoft.AspNetCore.Authentication; using System; using System.Collections.Generic; using System.Security.Claims; using System.Threading.Tasks; public class CustomClaimsTransformation : IClaimsTransformation { public async Task<ClaimsPrincipal> TransformAsync(ClaimsPrincipal principal) { var claims = principal.Claims.ToList(); // Add a custom claim claims.Add(new Claim("custom_claim", "custom_value")); var newIdentity = new ClaimsIdentity(claims, principal.Identity.AuthenticationType); var newPrincipal = new ClaimsPrincipal(newIdentity); return newPrincipal; } } ``` **JwtBearerOptions Configuration** --------------------------------- Next, let's configure `JwtBearerOptions` to use our custom claim transformation: ```csharp using Microsoft.AspNetCore.Authentication.JwtBearer; using Microsoft.Extensions.DependencyInjection; public void ConfigureServices(IServiceCollection services) { services.AddAuthentication(options => { options.DefaultAuthenticateScheme = JwtBearerDefaults.AuthenticationScheme; options.DefaultChallengeScheme = JwtBearerDefaults.AuthenticationScheme; }) .AddJwtBearer(options => { options.Audience = "your_audience"; options.Authority = "your_authority"; options.TokenValidationParameters = new TokenValidationParameters { ValidateIssuer = true, ValidateAudience = true, ValidateLifetime = true, ValidateIssuerSigningKey = true, IssuerSigningKey = new SymmetricSecurityKey(Encoding.UTF8.GetBytes("your_secret_key")) }; // Use our custom claim transformation options.Events = new JwtBearerEvents { OnTokenValidated = async context => { var claimsTransformation = context.HttpContext.RequestServices.GetService<IClaimsTransformation>(); var newPrincipal = await claimsTransformation.TransformAsync(context.Principal); context.Principal = newPrincipal; } }; }); // Register our custom claim transformation services.AddTransient<IClaimsTransformation, CustomClaimsTransformation>(); } ``` **Example Usage** ----------------- To test our custom claim transformation, we can create a simple controller that returns the claims of the authenticated user: ```csharp using Microsoft.AspNetCore.Mvc; using System.Security.Claims; [ApiController] [Route("api/[controller]")] public class ClaimsController : ControllerBase { [Authorize] [HttpGet] public IActionResult GetClaims() { var claims = User.Claims.ToList(); return Ok(claims); } } ``` When we make a GET request to `/api/claims`, we should see the custom claim `custom_claim` with value `custom_value` in the response. **Full Code Example** --------------------- Here is the full code example: ```csharp using Microsoft.AspNetCore.Authentication; using Microsoft.AspNetCore.Authentication.JwtBearer; using Microsoft.AspNetCore.Builder; using Microsoft.AspNetCore.Hosting; using Microsoft.Extensions.DependencyInjection; using System; using System.Collections.Generic; using System.Security.Claims; using System.Threading.Tasks; namespace CustomClaimTransformationExample { public class CustomClaimsTransformation : IClaimsTransformation { public async Task<ClaimsPrincipal> TransformAsync(ClaimsPrincipal principal) { var claims = principal.Claims.ToList(); // Add a custom claim claims.Add(new Claim("custom_claim", "custom_value")); var newIdentity = new ClaimsIdentity(claims, principal.Identity.AuthenticationType); var newPrincipal = new ClaimsPrincipal(newIdentity); return newPrincipal; } } public class Startup { public void ConfigureServices(IServiceCollection services) { services.AddAuthentication(options => { options.DefaultAuthenticateScheme = JwtBearerDefaults.AuthenticationScheme; options.DefaultChallengeScheme = JwtBearerDefaults.AuthenticationScheme; }) .AddJwtBearer(options => { options.Audience = "your_audience"; options.Authority = "your_authority"; options.TokenValidationParameters = new TokenValidationParameters { ValidateIssuer = true, ValidateAudience = true, ValidateLifetime = true, ValidateIssuerSigningKey = true, IssuerSigningKey = new SymmetricSecurityKey(Encoding.UTF8.GetBytes("your_secret_key")) }; // Use our custom claim transformation options.Events = new JwtBearerEvents { OnTokenValidated = async context => { var claimsTransformation = context.HttpContext.RequestServices.GetService<IClaimsTransformation>(); var newPrincipal = await claimsTransformation.TransformAsync(context.Principal); context.Principal = newPrincipal; } }; }); // Register our custom claim transformation services.AddTransient<IClaimsTransformation, CustomClaimsTransformation>(); services.AddControllers(); } public void Configure(IApplicationBuilder app, IWebHostEnvironment env) { app.UseRouting(); app.UseAuthentication(); app.UseAuthorization(); app.UseEndpoints(endpoints => { endpoints.MapControllers(); }); } } [ApiController] [Route("api/[controller]")] public class ClaimsController : ControllerBase { [Authorize] [HttpGet] public IActionResult GetClaims() { var claims = User.Claims.ToList(); return Ok(claims); } } } ``` Note that you should replace `your_audience`, `your_authority`, and `your_secret_key` with your actual JWT settings.

```csharp using Microsoft.AspNetCore.Authentication.JwtBearer; using Microsoft.AspNetCore.Authentication; using System; using System.IdentityModel.Tokens.Jwt; using System.Security.Claims; using System.Threading.Tasks; using Microsoft.Extensions.DependencyInjection; // Custom claim transformation public class CustomClaimsTransformation : IClaimsTransformation { public async Task<ClaimsPrincipal> TransformAsync(ClaimsPrincipal principal) { var claims = principal.Claims.ToList(); // Custom claim transformation logic var customClaim = new Claim("custom_claim", "custom_value"); claims.Add(customClaim); var newIdentity = new ClaimsIdentity(claims, principal.Identity.AuthenticationType); var newPrincipal = new ClaimsPrincipal(newIdentity); return await Task.FromResult(newPrincipal); } } // JwtBearerOptions handler with custom claim transformation public class CustomJwtBearerOptionsHandler : AuthenticationHandler<JwtBearerOptions> { private readonly IClaimsTransformation _claimsTransformation; public CustomJwtBearerOptionsHandler( IOptionsMonitor<JwtBearerOptions> options, ILoggerFactory logger, UrlEncoder encoder, ISystemClock clock, IClaimsTransformation claimsTransformation) : base(options, logger, encoder, clock) { _claimsTransformation = claimsTransformation; } protected override async Task<AuthenticateResult> HandleAuthenticateAsync() { var authenticateResult = await base.HandleAuthenticateAsync(); if (authenticateResult.Succeeded) { var transformedPrincipal = await _claimsTransformation.TransformAsync(authenticateResult.Principal); return AuthenticateResult.Success(new AuthenticationTicket(transformedPrincipal, authenticateResult.Properties, Scheme.Name)); } return authenticateResult; } } // DI registration public void ConfigureServices(IServiceCollection services) { services.AddTransient<IClaimsTransformation, CustomClaimsTransformation>(); services.AddAuthentication(options => { options.DefaultScheme = JwtBearerDefaults.AuthenticationScheme; }) .AddJwtBearer(options => { options.Audience = "your_audience"; options.Authority = "your_authority"; options.TokenValidationParameters = new TokenValidationParameters { ValidateIssuer = true, ValidateAudience = true, ValidateLifetime = true, ValidateIssuerSigningKey = true, IssuerSigningKey = new SymmetricSecurityKey("your_secret_key".Sha256()) }; }); services.AddSingleton<AuthenticationHandler<JwtBearerOptions>, CustomJwtBearerOptionsHandler>(); } ``` This implementation provides a custom `IClaimsTransformation` that adds a custom claim to the principal. The `CustomJwtBearerOptionsHandler` class inherits from `AuthenticationHandler<JwtBearerOptions>` and overrides the `HandleAuthenticateAsync` method to apply the custom claim transformation after successful authentication. The `CustomClaimsTransformation` and `CustomJwtBearerOptionsHandler` are registered in the DI container in the `ConfigureServices` method.