Support callback path based on IApplicationBuilder.Map paths

Is your feature request related to a problem? Please describe. The current callback path does not work together with path matches defined in IApplicationBuilder.Map. If adding the path match prefix from IApplicationBuilder.Map to the callback path, the callback endpoint becomes nested.

What area is it related to BankIdAuthenticationHandler

Describe the solution you’d like An option to add the path that I use in IApplicationBuilder.Map to the callback path. This can then be used in an override of ShouldHandleRequestAsync to handle the nested path.

Describe alternatives you’ve considered URL rewriting etc.

Additional context I have an open stack overflow question on how to work around the issue but it does not seem possible without changing the BankIdAuthenticationHandler.

https://stackoverflow.com/questions/58249177/using-remoteauthenticationhandler-callbackpath-with-iapplicationbuilder-path-mat?noredirect=1#comment102983312_58249177

I could spend the time implementing this if you think it it necessary and will make for a good addition.

[PeterOrneholm]

I would love to hear your thoughts before submitting a PR.

Had a look at your commit now, looks great from what I can see! You can make a PR so we can see that all tests are green etc. Also easier to comment if we were to find anything before merging 😃

Btw, GitHub has Draft PR:s nowdays. They are great for early feedback, but can’t be merged until the author (you in this case) says it’s ready to do so 😃

[span]

Very nice, I will dig right into it.

I am not sure why you think I need the IHttpContextAccessor though. There is an HttpContext available in the base class RemoteAuthenticationHandler that it receives in the InitializeAsync method.

It does not seems to affect the GrandId package:

private string GetAbsoluteUrl(string returnUrl)
{
    var absoluteUri = $"{Request.Scheme}://{Request.Host.ToUriComponent()}{Request.PathBase.ToUriComponent()}";
    return absoluteUri + returnUrl;
}

Is there any documentation that you know of that should be updated together with this change?