Two web application same origin how to embed one into another

I don't know whether I am asking at the right forum:

Two web applications A & B developed by two different companies in the .Net Framework.

Application A: is the parent application
Application B: is a child application to be deployed on the same server.

First thought to use iframe for Application B to make it part of Application A. In this case use postmessage for data transfer.

Kindly suggest another possible way. Can I use web API to embed HTML into another page? Which should support responsive behavior on all platform browsers including safari.