def create_proxy_ssl_context(
    ssl_version, cert_reqs, ca_certs=None, ca_cert_dir=None, ca_cert_data=None
):
    """
    Generates a default proxy ssl context if one hasn't been provided by the
    user.
    """
    ssl_context = create_urllib3_context(
        ssl_version=resolve_ssl_version(ssl_version),
        cert_reqs=resolve_cert_reqs(cert_reqs),
    )

    if (
        not ca_certs
        and not ca_cert_dir
        and not ca_cert_data
        and hasattr(ssl_context, "load_default_certs")
    ):
        ssl_context.load_default_certs()

    return ssl_context

    Generates a default proxy ssl context if one hasn't been provided by the
    user.
    
lib/urllib3/util/proxy.py