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: ca.go
    path of file: ./repos/kuma/pkg/plugins/ca/builtin
    
    the code of the file until where you have to start completion: package builtin

import (
	"crypto"
	"crypto/rand"
	"crypto/x509"
	"crypto/x509/pkix"
	"math/big"
	"net/url"
	"t
    
func newRootCa(mesh string, rsaBits int, certOpts ...certOptsFn) (*core_ca.KeyPair, error) {
	if rsaBits == 0 {
		rsaBits = util_rsa.DefaultKeySize
	}
	key, err := util_rsa.GenerateKey(rsaBits)
	if err != nil {
		return nil, errors.Wrap(err, "failed to generate a private key")
	}
	cert, err := newCACert(key, mesh, certOpts...)
	if err != nil {
		return nil, errors.Wrap(err, "failed to generate X509 certificate")
	}
	return util_tls.ToKeyPair(key, cert)
}