code: func ExtractChannelHeaderCertHash(msg proto.Message) []byte {
  	chdr, isChannelHeader := msg.(*cb.ChannelHeader)
  	if !isChannelHeader || chdr == nil {
  		return nil
  	}
  	return chdr.TlsCertHash
  }
docs: // ExtractChannelHeaderCertHash extracts the TLS cert hash from a channel header.