ASP.NET Core 2.0 Bearer Auth without Identity

Question

I thought I had a pretty simple goal in mind when I set out a day ago to implement a self-contained bearer auth webapi on .NET core 2.0, but I have yet to get anything remotely working. Here's a list of what I'm trying to do:

• Implement a bearer token protected webapi
• Issue tokens & refresh tokens from an endpoint in the same project
• Use the [Authorize] attribute to control access to api surface
• Not use ASP.Net Identity (I have much lighter weight user/membership reqs)

I'm totally fine with building identity/claims/principal in login and adding that to request context, but I've not seen a single example on how to issue and consume auth/refresh tokens in a Core 2.0 webapi without Identity. I've seen the 1.x MSDN example of cookies without Identity, but that didn't get me far enough in understanding to meet the requirements above.

I feel like this might be a common scenario and it shouldn't be this hard (maybe it's not, maybe just lack of documentation/examples?). As far as I can tell, IdentityServer4 is not compatible with Core 2.0 Auth, opendiddict seems to require Identity. I also don't want to host the token endpoint in a separate process, but within the same webapi instance.

Can anyone point me to a concrete example, or at least give some guidance as to what best steps/options are?

Answer 1

Did an edit to make it compatible with ASP.NET Core 2.0.

---

Firstly, some Nuget packages:

• Microsoft.AspNetCore.Authentication.JwtBearer
• Microsoft.AspNetCore.Identity
• System.IdentityModel.Tokens.Jwt
• System.Security.Cryptography.Csp

Then some basic data transfer objects.

// Presumably you will have an equivalent user account class with a user name.
public class User
{
    public string UserName { get; set; }
}

public class JsonWebToken
{
    public string access_token { get; set; }

    public string token_type { get; set; } = "bearer";

    public int expires_in { get; set; }

    public string refresh_token { get; set; }
}

Getting into the proper functionality, you'll need a login/token web method to actually send the authorization token to the user.

[Route("api/token")]
public class TokenController : Controller
{
    private ITokenProvider _tokenProvider;

    public TokenController(ITokenProvider tokenProvider) // We'll create this later, don't worry.
    {
        _tokenProvider = tokenProvider;
    }

    public JsonWebToken Get([FromQuery] string grant_type, [FromQuery] string username, [FromQuery] string password, [FromQuery] string refresh_token)
    {
        // Authenticate depending on the grant type.
        User user = grant_type == "refresh_token" ? GetUserByToken(refresh_token) : GetUserByCredentials(username, password);

        if (user == null)
            throw new UnauthorizedAccessException("No!");

        int ageInMinutes = 20;  // However long you want...

        DateTime expiry = DateTime.UtcNow.AddMinutes(ageInMinutes);

        var token = new JsonWebToken {
            access_token = _tokenProvider.CreateToken(user, expiry),
            expires_in   = ageInMinutes * 60
        };

        if (grant_type != "refresh_token")
            token.refresh_token = GenerateRefreshToken(user);

        return token;
    }

    private User GetUserByToken(string refreshToken)
    {
        // TODO: Check token against your database.
        if (refreshToken == "test")
            return new User { UserName = "test" };

        return null;
    }

    private User GetUserByCredentials(string username, string password)
    {
        // TODO: Check username/password against your database.
        if (username == password)
            return new User { UserName = username };

        return null;
    }

    private string GenerateRefreshToken(User user)
    {
        // TODO: Create and persist a refresh token.
        return "test";
    }
}

You probably noticed the token creation is still just "magic" passed through by some imaginary ITokenProvider. Define the token provider interface.

public interface ITokenProvider
{
    string CreateToken(User user, DateTime expiry);

    // TokenValidationParameters is from Microsoft.IdentityModel.Tokens
    TokenValidationParameters GetValidationParameters();
}

I implemented the token creation with an RSA security key on a JWT. So...

public class RsaJwtTokenProvider : ITokenProvider
{
    private RsaSecurityKey _key;
    private string _algorithm;
    private string _issuer;
    private string _audience;

    public RsaJwtTokenProvider(string issuer, string audience, string keyName)
    {
        var parameters = new CspParameters { KeyContainerName = keyName };
        var provider = new RSACryptoServiceProvider(2048, parameters);

        _key = new RsaSecurityKey(provider);

        _algorithm = SecurityAlgorithms.RsaSha256Signature;
        _issuer = issuer;
        _audience = audience;
    }

    public string CreateToken(User user, DateTime expiry)
    {
        JwtSecurityTokenHandler tokenHandler = new JwtSecurityTokenHandler();

        ClaimsIdentity identity = new ClaimsIdentity(new GenericIdentity(user.UserName, "jwt"));

        // TODO: Add whatever claims the user may have...

        SecurityToken token = tokenHandler.CreateJwtSecurityToken(new SecurityTokenDescriptor
        {
            Audience = _audience,
            Issuer = _issuer,
            SigningCredentials = new SigningCredentials(_key, _algorithm),
            Expires = expiry.ToUniversalTime(),
            Subject = identity
        });

        return tokenHandler.WriteToken(token);
    }

    public TokenValidationParameters GetValidationParameters()
    {
        return new TokenValidationParameters
        {
            IssuerSigningKey = _key,
            ValidAudience = _audience,
            ValidIssuer = _issuer,
            ValidateLifetime = true,
            ClockSkew = TimeSpan.FromSeconds(0) // Identity and resource servers are the same.
        };
    }
}

So you're now generating tokens. Time to actually validate them and wire it up. Go to your Startup.cs.

In ConfigureServices()

var tokenProvider = new RsaJwtTokenProvider("issuer", "audience", "mykeyname");
services.AddSingleton<ITokenProvider>(tokenProvider);

services.AddAuthentication(JwtBearerDefaults.AuthenticationScheme)
    .AddJwtBearer(options => {
        options.RequireHttpsMetadata = false;
        options.TokenValidationParameters = tokenProvider.GetValidationParameters();
    });

// This is for the [Authorize] attributes.
services.AddAuthorization(auth => {
    auth.DefaultPolicy = new AuthorizationPolicyBuilder()
        .AddAuthenticationSchemes(JwtBearerDefaults.AuthenticationScheme)
        .RequireAuthenticatedUser()
        .Build();
});

Then Configure()

public void Configure(IApplicationBuilder app)
{
    app.UseAuthentication();

    // Whatever else you're putting in here...

    app.UseMvc();
}

That should be about all you need. Hopefully I haven't missed anything.

The happy result is...

[Authorize] // Yay!
[Route("api/values")]
public class ValuesController : Controller
{
    // ...
}

Answer 2

Following on @Mitch answer: Auth stack changed quite a bit moving to .NET Core 2.0. Answer below is just using the new implementation.

using System.Text;
using Microsoft.AspNetCore.Authentication.JwtBearer;
using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Hosting;
using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.IdentityModel.Tokens;

namespace JwtWithoutIdentity
{
    public class Startup
    {
        public Startup(IConfiguration configuration)
        {
            Configuration = configuration;
        }

        public IConfiguration Configuration { get; }

        // This method gets called by the runtime. Use this method to add services to the container.
        public void ConfigureServices(IServiceCollection services)
        {
            services.AddAuthentication(JwtBearerDefaults.AuthenticationScheme)
                .AddJwtBearer(cfg =>
                {
                    cfg.RequireHttpsMetadata = false;
                    cfg.SaveToken = true;

                    cfg.TokenValidationParameters = new TokenValidationParameters()
                    {
                        ValidIssuer = "me",
                        ValidAudience = "you",
                        IssuerSigningKey = new SymmetricSecurityKey(Encoding.UTF8.GetBytes("rlyaKithdrYVl6Z80ODU350md")) //Secret
                    };

                });

            services.AddMvc();
        }

        // This method gets called by the runtime. Use this method to configure the HTTP request pipeline.
        public void Configure(IApplicationBuilder app, IHostingEnvironment env)
        {
            if (env.IsDevelopment())
            {
                app.UseDeveloperExceptionPage();
            }

            app.UseAuthentication();

            app.UseMvc();
        }
    }
}

Token Controller

using System;
using System.IdentityModel.Tokens.Jwt;
using System.Security.Claims;
using System.Text;
using System.Threading.Tasks;
using JwtWithoutIdentity.Models;
using Microsoft.AspNetCore.Authorization;
using Microsoft.AspNetCore.Mvc;
using Microsoft.IdentityModel.Tokens;

namespace JwtWithoutIdentity.Controllers
{
    public class TokenController : Controller
    {

        [AllowAnonymous]
        [Route("api/token")]
        [HttpPost]
        public async Task<IActionResult> Token(LoginViewModel model)
        {

            if (!ModelState.IsValid) return BadRequest("Token failed to generate");

            var user = (model.Password == "password" && model.Username == "username");

            if (!user) return Unauthorized();

            //Add Claims
            var claims = new[]
            {
                new Claim(JwtRegisteredClaimNames.UniqueName, "data"),
                new Claim(JwtRegisteredClaimNames.Sub, "data"),
                new Claim(JwtRegisteredClaimNames.Jti, Guid.NewGuid().ToString()),
            };

            var key = new SymmetricSecurityKey(Encoding.UTF8.GetBytes("rlyaKithdrYVl6Z80ODU350md")); //Secret
            var creds = new SigningCredentials(key, SecurityAlgorithms.HmacSha256);

            var token = new JwtSecurityToken("me",
                "you",
                claims,
                expires: DateTime.Now.AddMinutes(30),
                signingCredentials: creds);

            return Ok(new JsonWebToken()
            {
                access_token = new JwtSecurityTokenHandler().WriteToken(token),
                expires_in = 600000,
                token_type = "bearer"
            });
        }
    }
}

Values Controller

using System.Collections.Generic;
using Microsoft.AspNetCore.Authorization;
using Microsoft.AspNetCore.Mvc;

namespace JwtWithoutIdentity.Controllers
{
    [Route("api/[controller]")]
    public class ValuesController : Controller
    {
        // GET api/values
        [Authorize]
        [HttpGet]
        public IEnumerable<string> Get()
        {
            var name = User.Identity.Name;
            var claims = User.Claims;

            return new string[] { "value1", "value2" };
        }
    }
}

Hope this helps!