def authenticate(self,<EOL>username=None, password=None,<EOL>actions=None, response=None,<EOL>authorization=None):<EOL>
if response is None:<EOL><INDENT>with warnings.catch_warnings():<EOL><INDENT>_ignore_warnings(self)<EOL>response = self._sessions[<NUM_LIT:0>].get(self._base_url, verify=self._tlsverify)<EOL><DEDENT><DEDENT>if response.ok:<EOL><INDENT>return None<EOL><DEDENT>if response.status_code != requests.codes.unauthorized:<EOL><INDENT>raise exceptions.DXFUnexpectedStatusCodeError(response.status_code,<EOL>requests.codes.unauthorized)<EOL><DEDENT>if self._insecure:<EOL><INDENT>raise exceptions.DXFAuthInsecureError()<EOL><DEDENT>parsed = www_authenticate.parse(response.headers['<STR_LIT>'])<EOL>if username is not None and password is not None:<EOL><INDENT>headers = {<EOL>'<STR_LIT>': '<STR_LIT>' + base64.b64encode(_to_bytes_2and3(username + '<STR_LIT::>' + password)).decode('<STR_LIT:utf-8>')<EOL>}<EOL><DEDENT>elif authorization is not None:<EOL><INDENT>headers = {<EOL>'<STR_LIT>': authorization<EOL>}<EOL><DEDENT>else:<EOL><INDENT>headers = {}<EOL><DEDENT>if '<STR_LIT>' in parsed:<EOL><INDENT>info = parsed['<STR_LIT>']<EOL>if actions and self._repo:<EOL><INDENT>scope = '<STR_LIT>' + self._repo + '<STR_LIT::>' + '<STR_LIT:U+002C>'.join(actions)<EOL><DEDENT>elif '<STR_LIT>' in info:<EOL><INDENT>scope = info['<STR_LIT>']<EOL><DEDENT>else:<EOL><INDENT>scope = '<STR_LIT>'<EOL><DEDENT>url_parts = list(urlparse.urlparse(info['<STR_LIT>']))<EOL>query = urlparse.parse_qs(url_parts[<NUM_LIT:4>])<EOL>query.update({<EOL>'<STR_LIT>': info['<STR_LIT>'],<EOL>'<STR_LIT>': scope<EOL>})<EOL>url_parts[<NUM_LIT:4>] = urlencode(query, True)<EOL>url_parts[<NUM_LIT:0>] = '<STR_LIT>'<EOL>if self._auth_host:<EOL><INDENT>url_parts[<NUM_LIT:1>] = self._auth_host<EOL><DEDENT>auth_url = urlparse.urlunparse(url_parts)<EOL>with warnings.catch_warnings():<EOL><INDENT>_ignore_warnings(self)<EOL>r = self._sessions[<NUM_LIT:0>].get(auth_url, headers=headers, verify=self._tlsverify)<EOL><DEDENT>_raise_for_status(r)<EOL>rjson = r.json()<EOL>self.token = rjson['<STR_LIT>'] if '<STR_LIT>' in rjson else rjson['<STR_LIT>']<EOL>return self._token<EOL><DEDENT>self._headers = headers<EOL>return None<EOL>
Authenticate to the registry using a username and password,
an authorization header or otherwise as the anonymous user.

:param username: User name to authenticate as.
:type username: str

:param password: User's password.
:type password: str

:param actions: If you know which types of operation you need to make on the registry, specify them here. Valid actions are ``pull``, ``push`` and ``*``.
:type actions: list

:param response: When the ``auth`` function you passed to :class:`DXFBase`'s constructor is called, it is passed a HTTP response object. Pass it back to :meth:`authenticate` to have it automatically detect which actions are required.
:type response: requests.Response

:param authorization: ``Authorization`` header value.
:type authorization: str

:rtype: str
:returns: Authentication token, if the registry supports bearer tokens. Otherwise ``None``, and HTTP Basic auth is used (if the registry requires authentication).