Asymmetric JWT token with Go

generate key pair.sh

ssh-keygen -t rsa -b 2048 -f jwtRS256.key
openssl rsa -in jwtRS256.key -pubout -outform PEM -out jwtRS256.key.pub

poc.go

package main

import (
	"fmt"
	"io/ioutil"
	"time"

	jwt "gopkg.in/dgrijalva/jwt-go.v3"
)

func main() {

	token := jwt.NewWithClaims(jwt.SigningMethodRS256, jwt.MapClaims{
		"foo": "bar",
		"nbf": time.Date(2018, 06, 14, 12, 0, 0, 0, time.UTC).Unix(),
	})

	privateKeyString, err := ioutil.ReadFile("./jwtRS256.key")
	if err != nil {
		fmt.Printf("Error reading private key: %v", err)
		return
	}
	privateKey, err := jwt.ParseRSAPrivateKeyFromPEM(privateKeyString)
	if err != nil {
		fmt.Printf("Error converting private key: %v", err)
		return
	}
	tokenString, err := token.SignedString(privateKey)
	if err != nil {
		fmt.Printf("Error signing token: %v", err)
		return
	}

	fmt.Println("SIGNED:")
	fmt.Println(tokenString)

	// Verify:

	readToken, err := jwt.Parse(tokenString, func(token *jwt.Token) (interface{}, error) {
		if _, ok := token.Method.(*jwt.SigningMethodRSA); !ok {
			return nil, fmt.Errorf("Unexpected signing method: %v", token.Header["alg"])
		}

		publicKeyString, err := ioutil.ReadFile("./jwtRS256.key.pub")
		if err != nil {
			return nil, fmt.Errorf("Error reading public key: %v", err)
		}
		publicKey, err := jwt.ParseRSAPublicKeyFromPEM(publicKeyString)
		if err != nil {
			return nil, fmt.Errorf("Error converting public key: %v", err)
		}
		return publicKey, nil
	})

	if claims, ok := readToken.Claims.(jwt.MapClaims); ok && readToken.Valid {
		fmt.Println("VERIVIED:")
		fmt.Println(claims["foo"], claims["nbf"])
	} else {
		fmt.Println(err)
	}
}