New CertKey based on template and signed by signer, or self-signed if signer is nil.

NewCA creates a new dummy CA cert signed by signer, or self-signed if signer is nil.

NewCert creates a dummy server cert signed by signer, or self-signed if signer is nil.

NewServer creates a dummy client cert signed by signer, or self-signed if signer is nil.

CertKey holds a certificate struct, private key and DER encoded bytes.