Cannot register a U2F key with javascript & python APIs

I'm trying to implement U2F authentication devices in my django app. The primary issue now is, all of my front-end registration calls fail.

I'm using the u2f-api.js script and the python-u2flib-server python script to implement this.

I am following this pattern:

1) Generate a key/challenge with the u2flib

from u2flib_server import u2f
app_id = 'https://127.0.0.1'
reg = u2f.begin_registration(app_id)
print reg 
# {'registeredKeys': [], 
   'registerRequests': [{'challenge': u'pLzGmABMwBzQkco6INeFNuPsAG6KhgfVeYFeV0QBf1g', version': 'U2F_V2'}], 
   'appId': 'https://127.0.0.1'}

2) Register the key from browser

var reg_data = {'registeredKeys': [], 'registerRequests': [{'challenge': 'pLzGmABMwBzQkco6INeFNuPsAG6KhgfVeYFeV0QBf1g', 'version': 'U2F_V2'}], 'appId': 'https://127.0.0.1'}

u2f.register(reg_data['appId'], reg_data['registerRequests'], [], function(resp) { console.log(resp) });

This consistently returns a {errorCode: 2} response, which essentially means bad request. However, I'm unable to determine what part of this request is invalid.

I am using runserver_plus --cert certname to run my local webserver so the site is served via HTTPS. I've also tried using NGROK to access my site over HTTPS and attempted the same code. I consistently get the same response.

I would appreciate any help, pointers or guidance on my implementation as I've been struggling for a few days and the existing documentation around U2F libraries and implementations is pretty thin.

-- Update --

I've actually made slight progress here. I am able to receive the generate the key response. However, I am still unable to register this key with the python library.

I end up having something like this on the server side:

response = {'challenge': 'okGbjnbE2V9cT42X2wm-PA9pm7k3KpTETVEv2SqEUxE', 'registrationData': 'BRS5y7dFXs0O60o2cUFc-SZtKG3jibpFQGuwQDyTQkSWeQUNWn\\u2026bEwIhALYcM1NospvymAbv83lTlpLjaa2ICSFQv-5RYfzkPCc9', 'version': 'U2F_V2', 'clientData': 'eyJjaGFsbGVuZ2UiOiJva0dianBnRTJWOWNUNDJYMndtLVBBOX\\u2026R5cCI6Im5hdmlnYXRvci5pZC5maW5pc2hFbnJvbGxtZW50In0'}

register_request = {'registeredKeys': [], 'registerRequests': [{'challenge': 'okGbjpgE2V9cD32X2wm-PA9pm7k3KpKN5VEv2SqEUxE', 'version': 'U2F_V2'}], 'appId': 'https://127.0.0.1:8000'}

u2f.complete_registration(register_request, response)

However, this results in the following error:

Traceback (most recent call last):
  File "<console>", line 1, in <module>
  File "/usr/local/lib/python2.7/dist-packages/u2flib_server/u2f.py", line 45, in complete_registration
    return U2fRegisterRequest.wrap(request).complete(response, valid_facets)
  File "/usr/local/lib/python2.7/dist-packages/u2flib_server/model.py", line 419, in complete
    _validate_client_data(resp.clientData, req.challenge, Type.REGISTER,
  File "/usr/local/lib/python2.7/dist-packages/u2flib_server/model.py", line 339, in clientData
    return ClientData.wrap(self['clientData'])
  File "/usr/local/lib/python2.7/dist-packages/u2flib_server/model.py", line 261, in wrap
    return data if isinstance(data, cls) else cls(data)
  File "/usr/local/lib/python2.7/dist-packages/u2flib_server/model.py", line 328, in __init__
    super(ClientData, self).__init__(*args, **kwargs)
  File "/usr/local/lib/python2.7/dist-packages/u2flib_server/model.py", line 239, in __init__
    kwargs = json.loads(arg.decode('utf-8'))
  File "/usr/lib/python2.7/json/__init__.py", line 339, in loads
    return _default_decoder.decode(s)
  File "/usr/lib/python2.7/json/decoder.py", line 364, in decode
    obj, end = self.raw_decode(s, idx=_w(s, 0).end())
  File "/usr/lib/python2.7/json/decoder.py", line 382, in raw_decode
    raise ValueError("No JSON object could be decoded")
ValueError: No JSON object could be decoded

I'm stuck again! I've tried creating a json dumps out of the values before passing them to u2f.register to no avail- I get the exact same error.

from Cannot register a U2F key with javascript & python APIs