def _warn_about_tls_in_tls(
        self,
        underlying_transport: asyncio.Transport,
        req: "ClientRequest",
    ) -> None:
        """Issue a warning if the requested URL has HTTPS scheme."""
        if req.request_info.url.scheme != "https":
            return

        asyncio_supports_tls_in_tls = getattr(
            underlying_transport,
            "_start_tls_compatible",
            False,
        )

        if asyncio_supports_tls_in_tls:
            return

        warnings.warn(
            "An HTTPS request is being sent through an HTTPS proxy. "
            "This support for TLS in TLS is known to be disabled "
            "in the stdlib asyncio. This is why you'll probably see "
            "an error in the log below.\n\n"
            "It is possible to enable it via monkeypatching under "
            "Python 3.7 or higher. For more details, see:\n"
            "* https://bugs.python.org/issue37179\n"
            "* https://github.com/python/cpython/pull/28073\n\n"
            "You can temporarily patch this as follows:\n"
            "* https://docs.aiohttp.org/en/stable/client_advanced.html#proxy-support\n"
            "* https://github.com/aio-libs/aiohttp/discussions/6044\n",
            RuntimeWarning,
            source=self,
            # Why `4`? At least 3 of the calls in the stack originate
            # from the methods in this class.
            stacklevel=3,
        )
Issue a warning if the requested URL has HTTPS scheme.
lib/aiohttp/connector.py