kubernetes/cmd/kubeadm/app/phases/certs/renewal/filerenewer.go

type FileRenewer …

// NewFileRenewer returns a new certificate renewer that uses given CA cert and key for generating new certificates
func NewFileRenewer(caCert *x509.Certificate, caKey crypto.Signer) *FileRenewer { … }

// Renew a certificate using a given CA cert and key
func (r *FileRenewer) Renew(cfg *pkiutil.CertConfig) (*x509.Certificate, crypto.Signer, error) { … }