Allow to load SSL certfile and keyfile from a file-like object

Feature or enhancement

Proposal:

# Have a look in commit 7c3ddb5
# It should be possible to also load certfile and keyfile from embedded certificate strings
cert_file = io.BytesIO(SERVER_CERT_STRING.encode('utf-8'))
key_file = io.BytesIO(SERVER_KEY_ENCRYPTED_STRING.encode('utf-8'))
context.load_cert_chain(certfile=cert_file, keyfile=key_file, password=key_pass)

https://github.com/python/cpython/commit/7c3ddb51b969fbfc022c8b6a5d1c1a3c6861d481

It should be possible to also load certfile and keyfile from embedded certificate strings. At the moment the code only reads the certificates from files (filepath). But when you don't want to have the saved/written certificates on the storage you should be able to load them from embedded strings.

Would it possible to include this code to the latest cpython? I tested this code from commit 7c3ddb5 with cpython v3.8.10 and here it almost has worked directly and only few lines had to be adapted. But I also tried it with the latest cpython version and here in Visual Studio there are some warnings. I don't know why this functionality isn't included in the master branch because it adds useful and advanced functionalities.

Has this already been discussed elsewhere?

https://github.com/python/cpython/issues/60691

Links to previous discussion of this feature:

https://github.com/python/cpython/compare/main...jgehrcke:cpython:jgehrcke/address-issue-16487-sept17

Start by reviewing commit 7c3ddb5 and the discussion in issue 60691, then inspect the current SSLContext.load_cert_chain implementation and its tests. The change is complete when certificate and key file-like objects containing embedded strings are accepted with the existing password handling, with coverage for the proposed BytesIO usage.