Symptoms

I have configured HTTPRedirect in IIS and set landing URL to be my tasks page URL when the user browses the root URL https://k2forms.denallix.com. But it always throws error

401 - Unauthorized: Access is denied due to invalid credentials.
You do not have permission to view this directory or page using the credentials that you supplied.
 

Diagnoses

The HTTP Redirect may not be working because the top level site (that would usually be associated with the root URL "https://k2forms.denallix.com") does not have an Authentication Mode enabled. I believe, if you were to enable "Anonymous Authentication" on this top level site, then the IIS HTTP Redirect should work.

Please also note that "HTTP Redirect" is an IIS Configuration/Behavior for any ASP.net web application I had come across this suggestion while searching Microsoft's IIS forum:

https://forums.iis.net/t/1061576.aspx?401 2 Access Denied Unauthorize

Perhaps they can provide you with more information/possible configurations.
 

Resolution

This is an IIS setting. Perhaps consider the above suggestion or posting to the IIS forum.