Q:

Secure swagger docs page with username and password Asp Net Core 2.1

I am using Asp.Net Core 2.1 Web Api with Swashbuckle.aspnetcore.swagger
I want to secure api documentation page with username and password  before granting access.
Sample documention page 

To make sure its not accessible by the public

A:

Copied from mguinness's answer on Github:

In .NET Core you use middleware, instead of a DelegatingHandler:
public class SwaggerAuthorizedMiddleware
{
    private readonly RequestDelegate _next;

    public SwaggerAuthorizedMiddleware(RequestDelegate next)
    {
        _next = next;
    }

    public async Task Invoke(HttpContext context)
    {
        if (context.Request.Path.StartsWithSegments("/swagger")
            && !context.User.Identity.IsAuthenticated)
        {
            context.Response.StatusCode = StatusCodes.Status401Unauthorized;
            return;
        }

        await _next.Invoke(context);
    }
}

You will also need an extension method to help adding to pipeline:
public static class SwaggerAuthorizeExtensions
{
    public static IApplicationBuilder UseSwaggerAuthorized(this IApplicationBuilder builder)
    {
        return builder.UseMiddleware<SwaggerAuthorizedMiddleware>();
    }
}

Then add to Configure method in Startup.cs just before using Swagger:
app.UseSwaggerAuthorized();
app.UseSwagger();
app.UseSwaggerUi();

There's also a variant solution posted there how to do it with basic auth.

A:

I have found solution in git and applied to my project. its working as expected. 
Below code copied from there.
public class SwaggerBasicAuthMiddleware
{

private readonly RequestDelegate next;

    public SwaggerBasicAuthMiddleware(RequestDelegate next)
    {
        this.next = next;
    }

    public async Task InvokeAsync(HttpContext context)
    {
        //Make sure we are hitting the swagger path, and not doing it locally as it just gets annoying :-)
        if (context.Request.Path.StartsWithSegments("/swagger") && !this.IsLocalRequest(context))
        {
            string authHeader = context.Request.Headers["Authorization"];
            if (authHeader != null && authHeader.StartsWith("Basic "))
            {
                // Get the encoded username and password
                var encodedUsernamePassword = authHeader.Split(' ', 2, StringSplitOptions.RemoveEmptyEntries)[1]?.Trim();

                // Decode from Base64 to string
                var decodedUsernamePassword = Encoding.UTF8.GetString(Convert.FromBase64String(encodedUsernamePassword));

                // Split username and password
                var username = decodedUsernamePassword.Split(':', 2)[0];
                var password = decodedUsernamePassword.Split(':', 2)[1];

                // Check if login is correct
                if (IsAuthorized(username, password))
                {
                    await next.Invoke(context);
                    return;
                }
            }

            // Return authentication type (causes browser to show login dialog)
            context.Response.Headers["WWW-Authenticate"] = "Basic";

            // Return unauthorized
            context.Response.StatusCode = (int)HttpStatusCode.Unauthorized;
        }
        else
        {
            await next.Invoke(context);
        }
    }

    public bool IsAuthorized(string username, string password)
    {
        // Check that username and password are correct
        return username.Equals("SpecialUser", StringComparison.InvariantCultureIgnoreCase)
                && password.Equals("SpecialPassword1");
    }

    public bool IsLocalRequest(HttpContext context)
    {
        //Handle running using the Microsoft.AspNetCore.TestHost and the site being run entirely locally in memory without an actual TCP/IP connection
        if (context.Connection.RemoteIpAddress == null && context.Connection.LocalIpAddress == null)
        {
            return true;
        }
        if (context.Connection.RemoteIpAddress.Equals(context.Connection.LocalIpAddress))
        {
            return true;
        }
        if (IPAddress.IsLoopback(context.Connection.RemoteIpAddress))
        {
            return true;
        }
        return false;
    }
}
public static class SwaggerAuthorizeExtensions
    {
        public static IApplicationBuilder UseSwaggerAuthorized(this IApplicationBuilder builder)
        {
            return builder.UseMiddleware<SwaggerBasicAuthMiddleware>();
        }
    }

In Startup.cs
app.UseAuthentication(); //Ensure this like is above the swagger stuff

app.UseSwaggerAuthorized();
app.UseSwagger();
app.UseSwaggerUI();

