ASP.NET Core API: Authentication popup is not showing up in Swagger UI

Question

I have an ASP.NET Core Web API with Swagger integrated using Swashbuckle. I have successfully integrated authorization on Swagger UI using an operation filter, because I do not want to show padlock for anonymous APIs.

.OperationFilter<AuthorizeFilter>()

Inside the filter, I have registered basic auth security requirement for Swagger UI.

My problem is, even though authentication is happening in APIs on Swagger UI, I no longer see that nice authentication popup which is giving when click on the padlock icon.

Could someone answer, why I am not seeing the auth popup now?

Answer 1

Update 2023-04-17: Updated security definition type to Http as per @mimmoz81's suggestion

---

Assuming you have some endpoints that protected with [Authorize] attribute (can also be put on the controller).

[Route("")]
public class HelloController : ControllerBase
{
    [Authorize]
    [HttpGet("secure")]
    public IActionResult GetSomethingPrivate()
    {
        return Ok("secret");
    }

    [HttpGet("public")]
    public IActionResult GetSomethingPublic()
    {
        return Ok("hey");
    }
}

You need to define a security scheme suitable for your needs. But do not require it globally, instead add it inside an operation filter. Here I've added a simple token auth:

public void ConfigureServices(IServiceCollection services)
{
    services.AddControllers();
    services.AddSwaggerGen(c =>
    {
        c.SwaggerDoc("v1", new OpenApiInfo { Title = "ApiPlayground", Version = "v1" });
        c.AddSecurityDefinition("token", new OpenApiSecurityScheme
        {
            Type = SecuritySchemeType.Http,
            In = ParameterLocation.Header,
            Name = HeaderNames.Authorization,
            Scheme = "Bearer"
        });
        // dont add global security requirement
        // c.AddSecurityRequirement(/*...*/);
        c.OperationFilter<SecureEndpointAuthRequirementFilter>();
    });
}

And here's the operation filter which references the token auth scheme we've just created. It checks if the endpoint needs authentication, then adds the requirement.

internal class SecureEndpointAuthRequirementFilter : IOperationFilter
{
    public void Apply(OpenApiOperation operation, OperationFilterContext context)
    {
        if (!context.ApiDescription
            .ActionDescriptor
            .EndpointMetadata
            .OfType<AuthorizeAttribute>()
            .Any())
        {
            return;
        }

        operation.Security = new List<OpenApiSecurityRequirement>
        {
            new OpenApiSecurityRequirement
            {
                [new OpenApiSecurityScheme
                {
                    Reference = new OpenApiReference { Type = ReferenceType.SecurityScheme, Id = "token" }
                }] = new List<string>()
            }
        };
    }
}

When you run the app, it works as you expect:

So does the auth popup:

Bonus: using basic auth

Define a new security scheme with following values:

public void ConfigureServices(IServiceCollection services)
{
    // ...
    services.AddSwaggerGen(c =>
    {
        // ...
        // basic auth scheme (username + password)
        c.AddSecurityDefinition("basic", new OpenApiSecurityScheme
        {
            Type = SecuritySchemeType.Http,
            Scheme = "basic"
        });
        // dont add global security requirement
        // c.AddSecurityRequirement(/*...*/);
        c.OperationFilter<SecureEndpointAuthRequirementFilter>();
    });
}

Then update the operation filter to reference basic auth scheme:

internal class SecureEndpointAuthRequirementFilter : IOperationFilter
{
    public void Apply(OpenApiOperation operation, OperationFilterContext context)
    {
        if (!context.ApiDescription
            .ActionDescriptor
            .EndpointMetadata
            .OfType<AuthorizeAttribute>()
            .Any())
        {
            return;
        }

        operation.Security = new List<OpenApiSecurityRequirement>
        {
            new OpenApiSecurityRequirement
            {
                [new OpenApiSecurityScheme
                {
                    Reference = new OpenApiReference
                    {
                        Type = ReferenceType.SecurityScheme, 
                        Id = "basic" // <-- changed "token" -> "basic"
                    }
                }] = new List<string>()
            }
        };
    }
}

here's how the auth popup looks:

After logging in, requests include the correct Authorization header.