Crossdomain Iframe on webserver with Selenium

Need a webdeloper who can set up an iFrame in a web application with asp.net core using c#. Webserver is in Domain A. iFrame is referencing different domain, Domain B which is not in our control and therefore must have a work around. Iwould like to use c# code with Selenium using Chrome Driver in Headless mode to interact with the iFrame to retreive and insert data into iFrame. The examples below show how iFrame can access Domain B by making the calls from parent frame but I need Selenium to handle the back and forth traffic between iframe and Domain B. To complete task, code must funcion on webserver and not just in Visual Studio testing. I am willing to accept any solution that gets the job done. Since Domain B will have user ids and passwords to enter I do not want to expose this to the client computer and would like the login to be done by the webserver using the Selenium driver in Headless Mode.