TLS Mutual Authentication in Go

We need to generate “cert.pem” and “key.pem” so that we can build a TLS server, then we should load the certificate files in TLS client, so that the server and the client can mutually authenticate each other.

##### 1. TLS Server ---

package main

import (
    "log"
    "crypto/tls"
    "net"
    "bufio"
)

func main() {
    log.SetFlags(log.Lshortfile)

    cer, err := tls.LoadX509KeyPair("server.crt", "server.key")
    if err != nil {
        log.Println(err)
        return
    }

    config := &tls.Config{Certificates: []tls.Certificate{cer}}
    ln, err := tls.Listen("tcp", ":443", config) 
    if err != nil {
        log.Println(err)
        return
    }
    defer ln.Close()

    for {
        conn, err := ln.Accept()
        if err != nil {
            log.Println(err)
            continue
        }
        go handleConnection(conn)
    }
}

func handleConnection(conn net.Conn) {
    defer conn.Close()
    r := bufio.NewReader(conn)
    for {
        msg, err := r.ReadString('\n')
        if err != nil {
            log.Println(err)
            return
        }

        println(msg)

        n, err := conn.Write([]byte("world\n"))
        if err != nil {
            log.Println(n, err)
            return
        }
    }
}

##### 2. TLS Client ---

package main

import (
    "log"
    "crypto/tls"
)

func main() {
    log.SetFlags(log.Lshortfile)

    conf := &tls.Config{
         //InsecureSkipVerify: true,
    }

    conn, err := tls.Dial("tcp", "127.0.0.1:443", conf)
    if err != nil {
        log.Println(err)
        return
    }
    defer conn.Close()

    n, err := conn.Write([]byte("hello\n"))
    if err != nil {
        log.Println(n, err)
        return
    }

    buf := make([]byte, 100)
    n, err = conn.Read(buf)
    if err != nil {
        log.Println(n, err)
        return
    }

    println(string(buf[:n]))
}

Https Server

package main

import (
    "crypto/tls"
    "log"
    "net/http"
)

func main() {
    mux := http.NewServeMux()
    mux.HandleFunc("/", func(w http.ResponseWriter, req *http.Request) {
        w.Header().Add("Strict-Transport-Security", "max-age=63072000; includeSubDomains")
        w.Write([]byte("This is an example server.\n"))
    })
    cfg := &tls.Config{
        MinVersion:               tls.VersionTLS12,
        CurvePreferences:         []tls.CurveID{tls.CurveP521, tls.CurveP384, tls.CurveP256},
        PreferServerCipherSuites: true,
        CipherSuites: []uint16{
            tls.TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384,
            tls.TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA,
            tls.TLS_RSA_WITH_AES_256_GCM_SHA384,
            tls.TLS_RSA_WITH_AES_256_CBC_SHA,
        },
    }
    srv := &http.Server{
        Addr:         ":443",
        Handler:      mux,
        TLSConfig:    cfg,
        TLSNextProto: make(map[string]func(*http.Server, *tls.Conn, http.Handler), 0),
    }
    log.Fatal(srv.ListenAndServeTLS("tls.crt", "tls.key"))
}

Reference
http://www.levigross.com/2015/11/21/mutual-tls-authentication-in-go/
https://gist.github.com/denji/12b3a568f092ab951456
https://gist.github.com/spikebike/2232102