Customize OWIN/OAuth HTTP status code when rejecting a token request

Question

I've derived OAuthAuthorizationServerProvider in order to validate both clients and resource owners.

When I validate resource owners I find their credentials aren't valid, I call context.Rejected(), and HTTP response comes with HTTP/400 Bad Request status code while I would expect HTTP/401 Unauthorized.

How can I customize OAuthAuthorizationServerProvider's response HTTP status codes?

Answer 1

I follow a slightly different approach using System.Security.Authentication.AuthenticationException and an exception middleware.

The AuthenticationServerProvider:

public override async Task GrantResourceOwnerCredentials(OAuthGrantResourceOwnerCredentialsContext context)
    {
        using (UserManager<IdentityUser> userManager = _userManagerFactory())
        {
            IdentityUser user = await userManager.FindAsync(context.UserName, context.Password);

            if (user == null)
            {
                throw new AuthenticationException("The user name or password is incorrect.");
            }
            ....

The middleware:

public class ExceptionMiddleware : OwinMiddleware
    {
        public ExceptionMiddleware(OwinMiddleware next) : base(next)
        {
        }

        public override async Task Invoke(IOwinContext context)
        {
            try
            {
                await Next.Invoke(context);
            }
            catch (Exception ex)
            {
                HandleException(ex, context);
            }
        }

        private void HandleException(Exception ex, IOwinContext owinContext)
        {
            var errorDetails = new ErrorDetails()
            {
                Detail = ex.Message,
                Status = (int)HttpStatusCode.InternalServerError
            };

            switch (ex)
            {
                case AuthenticationException _:
                    errorDetails.Status = (int)HttpStatusCode.Unauthorized;
                    errorDetails.Title = "invalid_grant";
                    break;
                case [..]
                case Exception _:
                    errorDetails.Title = "An unexpected error occured";
                    break;
            }

            var serializedError = errorDetails.ToString();
            Log.Error($"Returning error response: {serializedError}");
            owinContext.Response.StatusCode = errorDetails.Status;
            owinContext.Response.ContentType = "application/json";
            owinContext.Response.Write(serializedError);
        }

        private class ErrorDetails
        {
            public int Status { get; set; }
            public string Title { get; set; }
            public string Detail { get; set; }

            public override string ToString()
            {
                return JsonSerializer.Serialize(this);
            }
        }

The app configuration:

public void Configure(IAppBuilder app)
    ....
        app.Use<ExceptionMiddleware>();
        // Configure auth here
    ....

    }

The result:

Answer 2

This is how we override the OwinMiddleware...first we created our own middleware on top of Owin...I think we had similar issue as you did.

First need to create a constant:

public class Constants
{
    public const string OwinChallengeFlag = "X-Challenge";
}

And we override the OwinMiddleware

public class AuthenticationMiddleware : OwinMiddleware
{
    public AuthenticationMiddleware(OwinMiddleware next) : base(next) { }

    public override async Task Invoke(IOwinContext context)
    {
        await Next.Invoke(context);

        if (context.Response.StatusCode == 400 && context.Response.Headers.ContainsKey(Constants.OwinChallengeFlag))
        {
            var headerValues = context.Response.Headers.GetValues(Constants.OwinChallengeFlag);
            context.Response.StatusCode = Convert.ToInt16(headerValues.FirstOrDefault());
            context.Response.Headers.Remove(Constants.OwinChallengeFlag);
        }

    }
}

In the startup.Auth file, we allowed the overrid of the Invoke Owin Commands

public void ConfigureAuth(IAppBuilder app)
    ....
        app.Use<AuthenticationMiddleware>(); //Allows override of Invoke OWIN commands
    ....

    }

And in the ApplicationOAuthProvider, we modified the GrantResourceOwnerCredentials.

public override async Task GrantResourceOwnerCredentials(OAuthGrantResourceOwnerCredentialsContext context)
    {
        using (UserManager<IdentityUser> userManager = _userManagerFactory())
        {
            IdentityUser user = await userManager.FindAsync(context.UserName, context.Password);

            if (user == null)
            {
                context.SetError("invalid_grant", "The user name or password is incorrect.");
                context.Response.Headers.Add(Constants.OwinChallengeFlag, new[] { ((int)HttpStatusCode.Unauthorized).ToString() }); //Little trick to get this to throw 401, refer to AuthenticationMiddleware for more
                //return;
            }
            ....