where PyOpenSSL is used?

Hello!

I can see pyopenssl dependency, but I cannot find where is it used. Could somebody point me?
Is it some indirect dependency?

UPDATE:
I can think that it is indirect dependency for https://github.com/google/openhtf/blob/v1.5.0/openhtf/output/callbacks/mfg_inspector.py which imports google.oauth2
But what is it? What is mfg-inspector.com ? Is it some internal google tool/service?