OAuth token expiration in MVC6 app - oauth-2.0

Question

So I have an MVC6 app that includes an identity server (using ThinkTecture's IdentityServer3) and an MVC6 web services application.
In the web services application I am using this code in Startup:
app.UseOAuthBearerAuthentication(options =>
{
options.Authority = "http://localhost:6418/identity";
options.AutomaticAuthentication = true;
options.Audience = "http://localhost:6418/identity/resources";
});
Then I have a controller with an action that has the Authorize attribute.
I have a JavaScript application that authenticates with the identity server, and then uses the provided JWT token to access the web services action.
This works, and I can only access the action with a valid token.
The problem comes when the JWT has expired. What I'm getting is what appears to be a verbose ASP.NET 500 error page, that returns exception information for the following exception:
System.IdentityModel.Tokens.SecurityTokenExpiredException
IDX10223: Lifetime validation failed. The token is expired.
I am fairly new to OAuth and securing Web APIs in general, so I may be way off base, but a 500 error doesn't seem appropriate to me for an expired token. It's definitely not friendly for a web service client.
Is this the expected behavior, and if not, is there something I need to do to get a more appropriate response?

Answer 1

Edit: this bug was fixed in ASP.NET Core RC2 and the workaround described in this answer is no longer needed.
Note: this workaround won't work on ASP.NET 5 RC1, due to this other bug. You can either migrate to the RC2 nightly builds or create a custom middleware that catches the exceptions thrown by the JWT bearer middleware and returns a 401 response:
app.Use(next => async context => {
try {
await next(context);
}
catch {
// If the headers have already been sent, you can't replace the status code.
// In this case, throw an exception to close the connection.
if (context.Response.HasStarted) {
throw;
}
context.Response.StatusCode = 401;
}
});
Sadly, that's how the JWT/OAuth2 bearer middleware (managed by MSFT) currently works by default, but it should be eventually fixed. You can see this GitHub ticket for more information: https://github.com/aspnet/Security/issues/411
Luckily, you can "easily" work around that by using the AuthenticationFailed notification:
app.UseOAuthBearerAuthentication(options => {
options.Notifications = new OAuthBearerAuthenticationNotifications {
AuthenticationFailed = notification => {
notification.HandleResponse();
return Task.FromResult<object>(null);
}
};
});