Manually decode OAuth bearer token in c#

Question

In my Web Api 2.2 OWIN based application I have a situation where I manually need to decode the bearer token but I don't know how to do this. This is my startup.cs

public class Startup
{
    public static OAuthAuthorizationServerOptions OAuthServerOptions { get; private set; }
    public static UnityContainer IoC;
    public void Configuration(IAppBuilder app)
    {
        //Set Auth configuration
        ConfigureOAuth(app);

        ....and other stuff
    }

    public void ConfigureOAuth(IAppBuilder app)
    {
        OAuthServerOptions = new OAuthAuthorizationServerOptions()
        {
            AllowInsecureHttp = true,
            TokenEndpointPath = new PathString("/token"),
            AccessTokenExpireTimeSpan = TimeSpan.FromDays(1),
            Provider = new AuthProvider(IoC.Resolve<IUserService>(), IoC.Resolve<IAppSettings>())
        };

        // Token Generation
        app.UseOAuthAuthorizationServer(OAuthServerOptions);
        app.UseOAuthBearerAuthentication(new OAuthBearerAuthenticationOptions());
    }
}

In my controller Im sending the bearer token as a parameter

[RoutePrefix("api/EP")]
public class EPController : MasterController
{
    [HttpGet]
    [AllowAnonymous]
    [Route("DC")]
    public async Task<HttpResponseMessage> GetDC(string token)
    {
        //Get the claim identity from the token here
        //Startup.OAuthServerOptions...

        //..and other stuff
    }
}

How to manually decode and get the claims from the token passed as a parameter?

NOTE: I know I can send the token in the header and use [Authorize] and (ClaimsIdentity)User.Identity etc but the question is how to read the token when it's not presented in the header.

Answer 1

I created a sample project for deserializing bearer tokens, which are encrypted using the MachineKeyDataProtector. You can take a look at the source code.

Bearer-Token-Deserializer

Answer 2

You can read JWT and create Principals and Identity object using the System.IdentityModel.Tokens.Jwt package - https://www.nuget.org/packages/System.IdentityModel.Tokens.Jwt/.

Here's a quick example that shows the options available when reading and validating the token,

    private ClaimsIdentity GetIdentityFromToken(string token, X509Certificate2 certificate)
    {  
        var tokenDecoder = new JwtSecurityTokenHandler();         
        var jwtSecurityToken = (JwtSecurityToken)tokenDecoder.ReadToken(token);

        SecurityToken validatedToken;

        var principal = tokenDecoder.ValidateToken(
            jwtSecurityToken.RawData,
            new TokenValidationParameters()
                {
                    ValidateActor = false,
                    ValidateIssuer = false,
                    ValidateAudience = false,
                    ValidateLifetime = false,
                    ValidateIssuerSigningKey = false,
                    RequireExpirationTime = false,
                    RequireSignedTokens = false,
                    IssuerSigningToken = new X509SecurityToken(certificate)
                },
            out validatedToken);

        return principal.Identities.FirstOrDefault();
    }

Answer 3

Just placing this here for others that may visit in the future. Solution found at https://long2know.com/2015/05/decrypting-owin-authentication-ticket/ is simpler.

Just 2 lines :

var secureDataFormat = new TicketDataFormat(new MachineKeyProtector());
AuthenticationTicket ticket = secureDataFormat.Unprotect(accessToken);



private class MachineKeyProtector : IDataProtector {
    private readonly string[] _purpose =
    {
        typeof(OAuthAuthorizationServerMiddleware).Namespace,
        "Access_Token",
        "v1"
    };

    public byte[] Protect(byte[] userData)
    {
        throw new NotImplementedException();
    }

    public byte[] Unprotect(byte[] protectedData)
    {
        return System.Web.Security.MachineKey.Unprotect(protectedData, _purpose);
    } }