func (c *Client) streamSizes() (*_SecPkgContext_StreamSizes, error) {
	var ss _SecPkgContext_StreamSizes
	ret := sspi.QueryContextAttributes(c.ctx.Handle, _SECPKG_ATTR_STREAM_SIZES, (*byte)(unsafe.Pointer(&ss)))
	if ret != sspi.SEC_E_OK {
		return nil, ret
	}
	return &ss, nil
}
TODO: maybe move all these into a separate package or something
package schannel
import (
	"syscall"
	"unsafe"
	"github.com/alexbrainman/sspi"
)