Adding a Required HTTP Header to Your Swagger UI With Swashbuckle

If you’re building ASP.NET Core Web APIs, then I hope you’ve heard of Swashbuckle – the tool to generate the Swagger UI automatically for all of your controllers to make manual testing your endpoints visual and simple.

Out of the box, the documentation helps you set up your UI, handle different ways to authenticate (which we will touch on in a later post), and have it all hooked up to your controllers. However, this only handles the most common cases of required requests with query string parameters and HTTP Body content.

In this post, we’ll look at a quick and easy way to also add fields for your custom HTTP Request Headers so you can fill them out while testing without having to do some funky stuff in the console.

Basic Swagger Setup

First thing’s first, install that puppy:

Package Manager : Install-Package Swashbuckle.AspNetCore
CLI : dotnet add package Swashbuckle.AspNetCore

Let’s first look at a simple swagger setup as our baseline before we add everything for our HTTP Header Field.

Startup.cs

//...
public void ConfigureServices(IServiceCollection services)
{
    // ...
    services.AddSwaggerGen(config =>
    {
        config.SwaggerDoc("v1", new Info { Title = "My API", Version = "V1" });
    });
    // ...
}

public void Configure(IApplicationBuilder app, IHostingEnvironment env)
{
    // ...
    app.UseMvc();

    app.UseSwagger();
    app.UseSwaggerUI(config =>
    {
        config.SwaggerEndpoint("/swagger/v1/swagger.json", "My API v1");
    });
    // ...
}
//...

This setup gives us all we need for our basic UI and wireup to our controllers!
Running this gives us our basic swagger at /swagger:

Adding Custom Headers

What we have to do now is add an OperationFilter to our swagger generation. These OperationFilters can do a whole lot and enable us to customize the swagger document created which is what drives the fields and info on the UI.

Let’s create a MyHeaderFilter and then add it to the AddSwaggerGen call.

MyHeaderFilter.cs

/// <summary>
/// Operation filter to add the requirement of the custom header
/// </summary>
public class MyHeaderFilter : IOperationFilter
{
    public void Apply(Operation operation, OperationFilterContext context)
    {
        if (operation.Parameters == null)
            operation.Parameters = new List<IParameter>();

        operation.Parameters.Add(new NonBodyParameter
        {
            Name = "MY-HEADER",
            In = "header",
            Type = "string",
            Required = true // set to false if this is optional
        });
    }
}

And now we need to update our Startup class:

Startup.cs

//...
public void ConfigureServices(IServiceCollection services)
{
    // ...
    services.AddSwaggerGen(config =>
    {
        config.SwaggerDoc("v1", new Info { Title = "My API", Version = "V1" });

        config.OperationFilter<MyHeaderFilter>();
    });
    // ...
}

Now when we run and navigate to our /swagger url, we can see:

When we fill out that field, we can now pull the value off the request header in our controller!

ContentController.cs

[Route("api/[controller]")]
public class ContentController : Controller
{
    public void Search([FromBody]InputModel model)
    {
        Console.WriteLine(Request.Headers["MY-HEADER"]);        
    }
}

In further posts, we’ll talk about adding Bearer Authentication, XML Comments, and More 🙂

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