Web Request to a Geocotex Essentials REST endpoint on a different domain secured with Windows Authentication

I'm wondering in workflow 4 or 5 if it's possible to programmatically access the Geocortex Essential REST or REST manager end point that hosted on another domain. The REST API is secured using Windows Integration with AD.

So far I have sorted out the CORS issue, but after I executed the workflow, when the Web Request activity tries to access the REST end point, the web browser pops up a window ask for log in. Is there a way to let the logon happening silently at the background, e.g. embed a token or username and password in the request header or something. thanks.

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