def proxy_manager_for(self, proxy, **proxy_kwargs):
        """Return urllib3 ProxyManager for the given proxy.

        This method should not be called from user code, and is only
        exposed for use when subclassing the
        :class:`HTTPAdapter <requests.adapters.HTTPAdapter>`.

        :param proxy: The proxy to return a urllib3 ProxyManager for.
        :param proxy_kwargs: Extra keyword arguments used to configure the Proxy Manager.
        :returns: ProxyManager
        :rtype: urllib3.ProxyManager
        """
        if proxy in self.proxy_manager:
            manager = self.proxy_manager[proxy]
        elif proxy.lower().startswith('socks'):
            username, password = get_auth_from_url(proxy)
            manager = self.proxy_manager[proxy] = SOCKSProxyManager(
                proxy,
                username=username,
                password=password,
                num_pools=self._pool_connections,
                maxsize=self._pool_maxsize,
                block=self._pool_block,
                **proxy_kwargs
            )
        else:
            proxy_headers = self.proxy_headers(proxy)
            manager = self.proxy_manager[proxy] = proxy_from_url(
                proxy,
                proxy_headers=proxy_headers,
                num_pools=self._pool_connections,
                maxsize=self._pool_maxsize,
                block=self._pool_block,
                **proxy_kwargs)

        return manager