Connecting to MS CRM 2016 Onpremise IFD using WebApi from C#

Hi All ,

I am trying to connect to my MS CRM 2016 Onpremise IFD instance from C# code using WebApi. while requesting for Token I am getting Following error.

Message = "The browser based authentication dialog failed to complete. Reason: The server understood the request, but is refusing to fulfill it."

does anybody have faced this error before ?

my code is as below

AuthenticationContext authContext = newAuthenticationContext(authority URL,false);

AuthenticationResult myres = authContext.AcquireToken(serviceUrl, clientId, newUri(redirectUrl));

on the 2nd line I am getting this error.

General Flow of our connecting to MS CRM from Browser is

1. when we type IFD Url in browser it shows one HTML Page where we need to enter email address , once clicked on Login , it goes to another Credential page where we have to enter user name and password in the format ( domain\username ) and then it goes to CRM

What can be wrong due to which I am getting above error ? any ideas ?

Thanks

Vilas