pip install で、[SSL: CERTIFICATE_VERIFY_FAILED] error

proxy内から、pip installを実行したところ、以下のようなSSLエラーが発生。

proxyサーバが ssl通信を一旦、decodeしているような気がしており、 このことが影響しているな気がします。

なので、以下のように --trusted-host オプションを追加し、解消。

DOS> .\python.exe -m pip install google-cloud-vision
WARNING: Retrying
  (Retry(total=4, connect=None, read=None, redirect=None, status=None))
  after connection broken by
  'SSLError(SSLCertVerificationError(1, '
  [SSL: CERTIFICATE_VERIFY_FAILED] certificate verify failed:
  self signed certificate in certificate chain (_ssl.c:1007)'))':
  /simple/google-cloud-vision/
＜略＞
Could not fetch URL https://pypi.org/simple/google-cloud-vision/:
  There was a problem confirming the ssl certificate:
  HTTPSConnectionPool(host='pypi.org', port=443):
  Max retries exceeded with url: /simple/google-cloud-vision/
  (Caused by SSLError(SSLCertVerificationError(1, '[SSL: CERTIFICATE_VERIFY_FAILED]
  certificate verify failed: self signed certificate
  in certificate chain (_ssl.c:1007)'))) - skipping
  
ERROR: Could not find a version that satisfies
  the requirement google-cloud-vision (from versions: none)
  
ERROR: No matching distribution found for google-cloud-vision

Could not fetch URL https://pypi.org/simple/pip/:
  There was a problem confirming the ssl certificate:
  HTTPSConnectionPool(host='pypi.org', port=443):
  Max retries exceeded with url: /simple/pip/
  (Caused by SSLError(SSLCertVerificationError(1, '[SSL: CERTIFICATE_VERIFY_FAILED]
  certificate verify failed:
  self signed certificate in certificate chain (_ssl.c:1007)'))) - skipping

DOS> .\python.exe -m pip \
   --trusted-host pypi.python.org \
   --trusted-host files.pythonhosted.org \
   --trusted-host pypi.org \
   install google-cloud-vision