urllib.error.URLError

[majidmc2]

When I want to install a napp, I get SSL verification error.
Example:

$ kytos napps install kytos/of_core
INFO    NApp kytos/of_core:
INFO      Downloading from NApps Server...
ERROR Error installing NApp.

Log:

Traceback (most recent call last):
  File "/usr/local/lib/python3.8/dist-packages/flask/app.py", line 2447, in wsgi_app
    response = self.full_dispatch_request()
  File "/usr/local/lib/python3.8/dist-packages/flask/app.py", line 1952, in full_dispatch_request
    rv = self.handle_user_exception(e)
  File "/usr/local/lib/python3.8/dist-packages/flask_cors/extension.py", line 161, in wrapped_function
    return cors_after_request(app.make_response(f(*args, **kwargs)))
  File "/usr/local/lib/python3.8/dist-packages/flask/app.py", line 1821, in handle_user_exception
    reraise(exc_type, exc_value, tb)
  File "/usr/local/lib/python3.8/dist-packages/flask/_compat.py", line 39, in reraise
    raise value
  File "/usr/local/lib/python3.8/dist-packages/flask/app.py", line 1950, in full_dispatch_request
    rv = self.dispatch_request()
  File "/usr/local/lib/python3.8/dist-packages/flask/app.py", line 1936, in dispatch_request
    return self.view_functions[rule.endpoint](**req.view_args)
  File "/usr/local/lib/python3.8/dist-packages/kytos-2021.1-py3.8.egg/kytos/core/api_server.py", line 500, in _install_napp
    if not self.napps_manager.install(napp, enable=True):
  File "/usr/local/lib/python3.8/dist-packages/kytos-2021.1-py3.8.egg/kytos/core/napps/manager.py", line 53, in install
    pkg_folder = napp.download()
  File "/usr/local/lib/python3.8/dist-packages/kytos-2021.1-py3.8.egg/kytos/core/napps/base.py", line 134, in download
    package_filename = urllib.request.urlretrieve(self.package_url)[0]
  File "/usr/lib/python3.8/urllib/request.py", line 247, in urlretrieve
    with contextlib.closing(urlopen(url, data)) as fp:
  File "/usr/lib/python3.8/urllib/request.py", line 222, in urlopen
    return opener.open(url, data, timeout)
  File "/usr/lib/python3.8/urllib/request.py", line 525, in open
    response = self._open(req, data)
  File "/usr/lib/python3.8/urllib/request.py", line 542, in _open
    result = self._call_chain(self.handle_open, protocol, protocol +
  File "/usr/lib/python3.8/urllib/request.py", line 502, in _call_chain
    result = func(*args)
  File "/usr/lib/python3.8/urllib/request.py", line 1367, in https_open
    return self.do_open(http.client.HTTPSConnection, req,
  File "/usr/lib/python3.8/urllib/request.py", line 1327, in do_open
    raise URLError(err)
urllib.error.URLError: <urlopen error [SSL: CERTIFICATE_VERIFY_FAILED] certificate verify failed: unable to get local issuer certificate (_ssl.c:1108)>