code: def test_proxy_auth(self):
      sign_in(
          self.username, self.api_key, plotly_proxy_authorization=True
      )
      headers = utils.get_headers()
      expected_headers = {
          "plotly-client-platform": "python {}".format(
              version.stable_semver()
          ),
          "authorization": "Basic Y25ldDpob29wbGE=",
          "plotly-authorization": "Basic Zm9vOmJhcg==",
          "content-type": "application/json",
      }
      self.assertEqual(headers, expected_headers)
  
imports: from __future__ import absolute_import
  import json
  from requests.exceptions import ConnectionError
  from plotly import version
  from chart_studio.api.utils import to_native_utf8_string
  from chart_studio.api.v2 import utils
  from chart_studio.exceptions import PlotlyRequestError
  from chart_studio.session import sign_in
  from chart_studio.tests.test_plot_ly.test_api import PlotlyApiTestCase
label_desc: Use image node_id 2 for calling the GetHeadersTest obj's underlying member method code with example usage: obj.test_proxy_auth() without return types