code: func (c *Context) Sizes() (uint32, uint32, uint32, uint32, error) {
  	var s _SecPkgContext_Sizes
  	ret := QueryContextAttributes(c.Handle, _SECPKG_ATTR_SIZES, (*byte)(unsafe.Pointer(&s)))
  	if ret != SEC_E_OK {
  		return 0, 0, 0, 0, ret
  	}
  	return s.MaxToken, s.MaxSignature, s.BlockSize, s.SecurityTrailer, nil
  }
docs: // Sizes queries the context for the sizes used in per-message functions.
  // It returns the maximum token size used in authentication exchanges, the
  // maximum signature size, the preferred integral size of messages, the
  // size of any security trailer, and any error.