HTTP Basic Access Authentication - Raw Implementation in .NET

Program.cs

using System.Text;
using Microsoft.Extensions.Primitives;
using Microsoft.Net.Http.Headers;

var app = WebApplication.Create(args);

string validUsername = "user1";
string validPassword = "password123";


app.MapGet("/", (HttpContext httpContext) =>
{
    if (!HasAuthorizationHeader(httpContext))
    {
        if (!httpContext.Request.Headers[HeaderNames.Authorization].Any())
        {
            httpContext.Response.Headers.Add(HeaderNames.WWWAuthenticate,
                new StringValues(new[] { "Basic", "realm=\"User Visible Realm\", charset=\"UTF-8\"" }));
            return Results.Unauthorized();
        }
    }

    var authorizationHeaders = httpContext.Request.Headers[HeaderNames.Authorization];
    if (authorizationHeaders.Count != 1)
    {
        return Results.Content("Expecting one Authorization header", statusCode: StatusCodes.Status401Unauthorized);
    }

    var authorizationHeader = authorizationHeaders[0]!;

    if (!authorizationHeader.StartsWith("Basic "))
    {
        return Results.Content("'Basic ' authorization scheme expected", statusCode: StatusCodes.Status401Unauthorized);
    }

    var encodedCredentials = authorizationHeader.Replace("Basic ", String.Empty);

    var decodedBytes = Convert.FromBase64String(encodedCredentials);
    var credentials = Encoding.UTF8.GetString(decodedBytes).Split(":");
    var username = credentials[0];
    var password = credentials[1];

    if (username == validUsername && password == validPassword)
    {
        return Results.Text("User Authorized! <br/> <br/> <b>The Permitted content authorized for user</b>", "text/html");
    }

    return Results.Content("Invalid credentials", statusCode: StatusCodes.Status401Unauthorized);

});

app.UseHttpsRedirection();

app.Run();
bool HasAuthorizationHeader(HttpContext httpContext)
{
    return httpContext.Request.Headers.ContainsKey(HeaderNames.Authorization);
}