I successfully (with much frustration) got our c# embedded signing to work on our site, however, that was before I tested with Safari on a Mac. Safari does not allow Third
Since you have embedding working in terms of generating a URL token, it's up to you how to access that URL. We've seen developers write their own programs to view where they have complete control over the iFrame and can do whatever they like with it, and another solution we've seen is to use a web browser control.
see this SO link