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
The only workaround that I know of is to pop up a new browser window. I know there is work being done to make it work without cookies, but at this time the new browser window is your only choice.
Sorry about that.