Network actions Because there is no browser provided insight to browser actions related to the FedCM API callsthe advice is to use an application such as Fiddler, Charles Proxy, Burp suite, Proxy Man etc. ProxyMan handles the SSL handling for you relatively easily and is free.
Issues with testing
The "developer tools" fails to show any information about the browser's actions in response to the API calls. Despite requests to our browser contacts, there is no movement here.