A large number of brownie points to anyone can shed some light on this as it would allow me to embed the Kindle Cloud reader in Obsidian.
I can get Kindle Cloud Reader to show up in iFrame in Obsidian using the standard iFrame code. (Note that you must log in.)
<iframe width="800" height="600" src="https://read.amazon.com/"></iframe>
However, there is a Library button that shows up in the browser, Chrome, for example, that does not show up in Obsidian. See screen clips below. Once you get into a book you cannot go back to the Library without this button.
In Chrome:

In Obsidian:

Obsidian 0.12.3
Windows 10 Pro 20H2, OS build 19042.985
Surface Pro 5
Addendum: By exposing the Inspector, I was able to to clear the session and cache re-login to Cloud Reader, getting back to the Library. Can one invoke clearing the session and cache from a Button, perhaps? This would still be cumbersome, of course, but better then opening the inspector each time.