ASP.NET Core 2.0 Bearer Auth without Identity

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
{
    // ...
}