Fix #390: Use code to generate certificates for client & server

[GuillaumeSmaha]

I take inspiration from https://go.dev/src/crypto/tls/generate_cert.go to generate the certificate.

certGetCertificate allows more complex pattern like generating a CA and signing another certificate with:

	ca, _ _, err := certGetCertificate(&certConfig{
		isCA: true,
		extKeyUsage: []x509.ExtKeyUsage{x509.ExtKeyUsageServerAuth},
	})

	_, serverCertPEM, serverKeyPEM, err := certGetCertificate(&certConfig{
                signCA: ca
		hosts: []string{
			"0.0.0.0",
			"localhost",
		},
		extKeyUsage: []x509.ExtKeyUsage{x509.ExtKeyUsageServerAuth},
	})

I use ioutil.WriteFile instead of os.WriteFile to be compatible with older go version.

[GuillaumeSmaha]

@jpillora Is it what you looked for ?

[jpillora]

Sorry I triggered the tests and then forgot about this PR

Looks good from my phone! Hopefully will get some time tomorrow to look at it properly

Thank you for your work 😁

[GuillaumeSmaha]

Sorry I triggered the tests and then forgot about this PR

Looks good from my phone! Hopefully will get some time tomorrow to look at it properly

Thank you for your work grin

Your are welcome. Thanks for building this project :)

[jpillora]

Merged :) Thanks again!