Validation of SSL Certificates with Go

main1go

package main

// Checking for an SSL certificate

import (
	"crypto/tls"
)

func main() {

	// Error Example
	_, err := tls.Dial("tcp", "example.com:80", nil)

	if err != nil {
		panic("Server doesn't support SSL certificate err: " + err.Error())
	}

	// Valid Example
	_, err = tls.Dial("tcp", "microsoft.com:443", nil)

	if err != nil {
		panic("Server doesn't support SSL certificate err: " + err.Error())
	}
}

main2.go

package main

// Checking the hostname against the SSL certificate

import (
	"crypto/tls"
)

func main() {
	conn, err := tls.Dial("tcp", "microsoft.com:443", nil)
	if err != nil {
		panic("Server doesn't support SSL certificate err: " + err.Error())
	}

	// Error Example
	err = conn.VerifyHostname("microsoftz")
	if err != nil {
		panic("Hostname doesn't match with certificate: " + err.Error())
	}

	// Valid Example
	err = conn.VerifyHostname("microsoft.com")
	if err != nil {
		panic("Hostname doesn't match with certificate: " + err.Error())
	}
}

main3.go

package main

// Checking the expiration date of an SSL certificate

import (
	"crypto/tls"
	"fmt"
	"time"
)

func main() {
	conn, err := tls.Dial("tcp", "microsoft.com:443", nil)
	if err != nil {
		panic("Server doesn't support SSL certificate err: " + err.Error())
	}

	err = conn.VerifyHostname("microsoft.com")
	if err != nil {
		panic("Hostname doesn't match with certificate: " + err.Error())
	}
	expiry := conn.ConnectionState().PeerCertificates[0].NotAfter
	fmt.Printf("Issuer: %s\nExpiry: %v\n", conn.ConnectionState().PeerCertificates[0].Issuer, expiry.Format(time.RFC850))
}