Support loading keys and certificates as variables (bytes) in particular in the load_cert_chain function

Proposal:

In MutualTLS Authentication scenarios it's useful to maintain client credential (private_key) confidentiality by allowing loading of the credential from encrypted key archives for example PKCS12. Python Cryptography and other modules allow loading of private keys into memory and at present we need to write those sensitive files to disk temporarily in order to load them into our TLS Client context.

This appears to be the existing code https://github.com/python/cpython/blob/a9c304cf020e2fa3ae78fd88359dfc808c9dd639/Modules/_ssl.c#L3899

    if (keyfile && !PyUnicode_FSConverter(keyfile, &keyfile_bytes)) {
        if (PyErr_ExceptionMatches(PyExc_TypeError)) {
            PyErr_SetString(PyExc_TypeError,
                            "keyfile should be a valid filesystem path");
        }
        goto error;
    }

Has this already been discussed elsewhere?

There is one somewhat similar feature request relating to loading from PKCS11 tokens. This is not related.

Links to previous discussion of this feature:

No response

Modules/_ssl.c の load_cert_chain の実装と、issue に示されているファイルシステムパスの変換から始めます。現在の関数がキーと証明書のパスをどのように受け入れているかを確認し、インメモリのバイト入力に必要な API とテストカバレッジを決定します。認証情報を一時的な機密ファイルを必要とせずにバイトから読み込めるようになれば完了です。