UserAgent: Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/70.0.3538.77 Safari/537.36

Steps to reproduce the problem:
1. The attached file needs to be run over https in order to work. I've hosted it on https://test.fairy.ninja:8443/trails/credentialmanagement.html (using self-signed cert, sorry about that). 
2. Click "Linky", you should get a "success" message in the console. 
3. Starting a headless chrome session using the command "google-chrome --headless --remote-debugging-port=9222 --ignore-certificate-errors --enable-features=NetworkService"
4. Visit 127.0.0.1:9222 and click the about:blank tab (or any tab). 
5. Browse to https://test.fairy.ninja:8443/trails/credentialmanagement.html and click "Linky". This time you will not get a "success" message but rather a "DOMException: The user agent does not support public key credentials." error.

What is the expected behavior?
Getting "success" both in "regular" Chrome and headless Chrome. 

What went wrong?
DOMException: The user agent does not support public key credentials.

Did this work before? N/A 

Does this work in other browsers? Yes

Chrome version: 70.0.3538.77  Channel: stable
OS Version: Ubuntu 18.04.1
Flash Version: 

After some Googling I stumbled upon this (https://chromium.googlesource.com/chromium/src/third_party/+/master/blink/renderer/modules/credentialmanager/scoped_promise_resolver.cc) which leads me to believe that this feature is simply not implemented when in headless mode.
 

Deleted: credentialmanagement.html 375 bytes

credentialmanagement.html 375 bytes View Download