aspnet-api-patterns

ASP.NET Core API Patterns

Reference for API development. Used by dnp-api-scaffolder and dnp-planner.

Controller vs Minimal API Decision

Factor	Controllers	Minimal API
Team familiarity	Traditional .NET teams	Modern, lightweight preference
OpenAPI support	Full attribute support	Requires explicit configuration
Filters/middleware	Rich filter pipeline	Endpoint filters (simpler)
File organization	One controller per resource	Endpoint groups or single file
Testability	Via WebApplicationFactory	Same
Performance	Slightly slower (reflection)	Slightly faster

Controller Pattern

[ApiController]
[Route("api/[controller]")]
[Produces("application/json")]
public class UsersController : ControllerBase
{
    [HttpGet("{id:int}")]
    [ProducesResponseType(typeof(UserResponse), StatusCodes.Status200OK)]
    [ProducesResponseType(StatusCodes.Status404NotFound)]
    public async Task<IActionResult> GetById(int id, CancellationToken ct)
    {
        var user = await _userService.GetByIdAsync(id, ct);
        return user is null ? NotFound() : Ok(user);
    }

    [HttpPost]
    [ProducesResponseType(typeof(UserResponse), StatusCodes.Status201Created)]
    [ProducesResponseType(typeof(ValidationProblemDetails), StatusCodes.Status400BadRequest)]
    public async Task<IActionResult> Create(CreateUserRequest request, CancellationToken ct)
    {
        var user = await _userService.CreateAsync(request, ct);
        return CreatedAtAction(nameof(GetById), new { id = user.Id }, user);
    }
}

Error Handling

Global Exception Handler (preferred)

app.UseExceptionHandler(app => app.Run(async context =>
{
    var exception = context.Features.Get<IExceptionHandlerFeature>()?.Error;
    var problemDetails = new ProblemDetails
    {
        Status = StatusCodes.Status500InternalServerError,
        Title = "An error occurred"
    };
    context.Response.StatusCode = problemDetails.Status.Value;
    await context.Response.WriteAsJsonAsync(problemDetails);
}));

Use ProblemDetails for all error responses (RFC 7807)

Authentication Patterns

JWT Bearer

builder.Services.AddAuthentication(JwtBearerDefaults.AuthenticationScheme)
    .AddJwtBearer(options =>
    {
        options.TokenValidationParameters = new TokenValidationParameters
        {
            ValidateIssuer = true,
            ValidateAudience = true,
            ValidateLifetime = true,
            ValidateIssuerSigningKey = true,
            ValidIssuer = config["Jwt:Issuer"],
            ValidAudience = config["Jwt:Audience"],
            IssuerSigningKey = new SymmetricSecurityKey(Encoding.UTF8.GetBytes(config["Jwt:Key"]!))
        };
    });

Middleware Order (critical)

app.UseExceptionHandler();
app.UseHttpsRedirection();
app.UseAuthentication();
app.UseAuthorization();
app.UseRateLimiter();
app.MapControllers();