ASP.NET Core Web API Authentication

I'm struggling with how to set up authentication in my web service. The service is build with the ASP.NET Core web api.

All my clients (WPF applications) should use the same credentials to call the web service operations.

After some research, I came up with basic authentication - sending a username and password in the header of the HTTP request. But after hours of research, it seems to me that basic authentication is not the way to go in ASP.NET Core.

Most of the resources I found are implementing authentication using OAuth or some other middleware. But that seems to be oversized for my scenario, as well as using the Identity part of ASP.NET Core.

So what is the right way to achieve my goal - simple authentication with username and password in a ASP.NET Core web service?

Thanks in advance!

Now, after I was pointed in the right direction, here's my complete solution:

This is the middleware class which is executed on every incoming request and checks if the request has the correct credentials. If no credentials are present or if they are wrong, the service responds with a 401 Unauthorized error immediately.

public class AuthenticationMiddleware
{
    private readonly RequestDelegate _next;

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

    public async Task Invoke(HttpContext context)
    {
        string authHeader = context.Request.Headers["Authorization"];
        if (authHeader != null && authHeader.StartsWith("Basic"))
        {
            //Extract credentials
            string encodedUsernamePassword = authHeader.Substring("Basic ".Length).Trim();
            Encoding encoding = Encoding.GetEncoding("iso-8859-1");
            string usernamePassword = encoding.GetString(Convert.FromBase64String(encodedUsernamePassword));

            int seperatorIndex = usernamePassword.IndexOf(':');

            var username = usernamePassword.Substring(0, seperatorIndex);
            var password = usernamePassword.Substring(seperatorIndex + 1);

            if(username == "test" && password == "test" )
            {
                await _next.Invoke(context);
            }
            else
            {
                context.Response.StatusCode = 401; //Unauthorized
                return;
            }
        }
        else
        {
            // no authorization header
            context.Response.StatusCode = 401; //Unauthorized
            return;
        }
    }
}

The middleware extension needs to be called in the Configure method of the service Startup class

public void Configure(IApplicationBuilder app, IHostingEnvironment env, ILoggerFactory loggerFactory)
{
    loggerFactory.AddConsole(Configuration.GetSection("Logging"));
    loggerFactory.AddDebug();

    app.UseMiddleware<AuthenticationMiddleware>();

    app.UseMvc();
}

And that's all! :)

A very good resource for middleware in .Net Core and authentication can be found here: https://www.exceptionnotfound.net/writing-custom-middleware-in-asp-net-core-1-0/

You can implement a middleware which handles Basic authentication.

public async Task Invoke(HttpContext context)
{
    var authHeader = context.Request.Headers.Get("Authorization");
    if (authHeader != null && authHeader.StartsWith("basic", StringComparison.OrdinalIgnoreCase))
    {
        var token = authHeader.Substring("Basic ".Length).Trim();
        System.Console.WriteLine(token);
        var credentialstring = Encoding.UTF8.GetString(Convert.FromBase64String(token));
        var credentials = credentialstring.Split(':');
        if(credentials[0] == "admin" && credentials[1] == "admin")
        {
            var claims = new[] { new Claim("name", credentials[0]), new Claim(ClaimTypes.Role, "Admin") };
            var identity = new ClaimsIdentity(claims, "Basic");
            context.User = new ClaimsPrincipal(identity);
        }
    }
    else
    {
        context.Response.StatusCode = 401;
        context.Response.Headers.Set("WWW-Authenticate", "Basic realm=\"dotnetthoughts.net\"");
    }
    await _next(context);
}

This code is written in a beta version of asp.net core. Hope it helps.