OAuth on Enterprise Server unexpected behaviour

[ThomasC]

I'm hoping someone can help me, I'm trying to implement esri's oAuth solution as described here:
Implement user authentication | Overview | ArcGIS Maps SDK for JavaScript 4.27 | ArcGIS Developers

This is the first time implementing onto an Enterprise server rather then Arcgis Online.

i'm running the code as is with the AppID and portalURL configered in the OAuthInfo object.
I have two feature layers hosted on their server that require a login to test authentication.

But I am getting the below popup which appears even if I have the OAuth code commented out or not.

Anyone know what is going on?

[Thomas_Puthusserry]

Hi @ThomasC  have you managed to find a solution to this? I have same issue with login to enterprise portal (it works fine in AGOL). 

Thanks Thomas Puthusserry