You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: auth_scram.go
    path of file: ./repos/tegola/vendor/github.com/jackc/pgconn
    
    the code of the file until where you have to start completion: // SCRAM-SHA-256 authentication
//
// Resources:
//   https://tools.ietf.org/html/rfc5802
//   https://tools.ietf.org/html/rfc8265
//   https://www.postgresql.org/docs/current/sasl-authentication.html
//
// Inspiratio
    
func (sc *scramClient) recvServerFinalMessage(serverFinalMessage []byte) error {
	if !bytes.HasPrefix(serverFinalMessage, []byte("v=")) {
		return errors.New("invalid SCRAM server-final-message received from server")
	}

	serverSignature := serverFinalMessage[2:]

	if !hmac.Equal(serverSignature, computeServerSignature(sc.saltedPassword, sc.authMessage)) {
		return errors.New("invalid SCRAM ServerSignature received from server")
	}

	return nil
}