Add Support for OAuth Mutual TLS (draft-ietf-oauth-mtls)

[danielfett]

OAuth Mutual TLS is on track to become an IETF standard. It will be used in many high-risk scenarios, including Open Banking (see OpenID FAPI), e-health applications, and e-government applications. This patch adds support for client authentication via MTLS.

[coveralls]

Coverage decreased (-0.03%) to 90.462% when pulling a8f45a7 on danielfett:master into 792f184 on requests:master.

[singingwolfboy]

This looks like a great start! However, we need an automated test covering this change, and an entry in the HISTORY.rst file.

Let me know if you have any difficulty with writing this test. I think you'll want to mock the requests library, and verify that it's being called with the cert parameter.

[danielfett]

Added tests and HISTORY.rst entry.

[singingwolfboy]

Looks great! Thank you! 🎉