UseElmahExceptionPage under IIS sub-application

[FuncLun]

It appears that the Elmah Exception Page does not work properly while running under an IIS sub application.

Assume running an app under IIS and the "/" application is not running MVC. But an mvc6 application is deployed to "/mvc6". Using the default options for Services.AddElmah() and app.UseElmahExceptionPage() works fine while accessing the error page (i.e. "/mvc/elmah"). But, when an exception occurs, the redirect url is "/elmah/detail/{guid}", which is to the root application.

Updating the ElmahOptions.Path to various values does not resolve the issue.

"elmah"
Same behavior as not setting
Elmah error page works at "/mvc6/elmah"
Elmah redirect is to "/elmah/detail/{guid}" and is a 404
If I modify the error redirect to "/mvc6/elmah/detail/{guid}", the error page displays
The detail page incorrectly updates the URL. If the exception occured on "/mvc6/controller/action", the url becomes "/controller/action". (This appears to be a .pushState() and not a redirect.)

"~/elmah"
Elmah error page does not work
Elmah redirect is to ~/elmah/detail/{guid} (the ~ is not translated)

"/mvc6/elmah"
Elmah error page works at /mvc6/mvc6/elmah
Elmah redirect is to /mvc6/elmah/detail/{guid} and is a 404

A possible fix is to modify ErrorLogMiddleware.InvokeAsync(HttpContext context) to and replace "~/" with HttpContext.Request.PathBase.

[FuncLun]

I have fixed this in 0350dd2. Waiting for PR review/completion.