JWT Go - RSA generation and validation example

main.go

// Generate keys (based in https://gist.github.com/nghiaht/224f7fe04ea591c6d2fddbee6c173379)

// Gen private keys:
// openssl genpkey -algorithm RSA -out private.pem -pkeyopt rsa_keygen_bits:2048

// Gen public keys:
// openssl rsa -pubout -in private.pem -out public_key.pem

package main

import (
	"fmt"
	"github.com/dgrijalva/jwt-go"
	"io/ioutil"
	"time"
)

type MyCustomClaims struct {
	Foo string `json:foo`
	*jwt.StandardClaims
}

func genToken() (string, error) {
	privateKey, _ := ioutil.ReadFile("keys/private.pem")
	parsedPrivateKey, err := jwt.ParseRSAPrivateKeyFromPEM(privateKey)

	if err != nil {
		fmt.Printf("Parse error private key %s\n\n", err)
	}

	// Create the token
	token := jwt.New(jwt.GetSigningMethod("RS256"))

	claims := make(jwt.MapClaims)

	claims["exp"] = time.Now().Add(time.Hour * time.Duration(1)).Unix()
	claims["foo"] = "bar"

	token.Claims = claims

	// Sign and get the complete encoded token as a string
	tokenString, err := token.SignedString(parsedPrivateKey)

	if err != nil {
		fmt.Printf("Err: %s\n\n", err)
		return "", err
	}

	return tokenString, nil
}

func validateToken(token string) error {
	publicKey, _ := ioutil.ReadFile("keys/public_key.pem")
	parsedPublicKey, err := jwt.ParseRSAPublicKeyFromPEM(publicKey)

	if err != nil {
		fmt.Printf("Parse error public key %s\n\n", err)
	}

	keyLookupFunc := func(token *jwt.Token) (interface{}, error) {
		return parsedPublicKey, nil
	}

	tokenResult, err := jwt.ParseWithClaims(token, &MyCustomClaims{}, keyLookupFunc)

	if err == nil {
		claims := tokenResult.Claims.(*MyCustomClaims)
		fmt.Printf("Token for user %v expires %v\n\n", claims.Foo, claims.StandardClaims.ExpiresAt)
	}

	if err == nil && tokenResult.Valid {
		return nil
	} else {
		return fmt.Errorf("Token invalid: err: %s\n\n", err)
	}
}

func main() {
	tokenString, err := genToken()

	if err != nil {
		fmt.Printf("Error when generating token %s\n\n", err)
		return
	}

	err = validateToken(tokenString)

	if err != nil {
		fmt.Printf("Error to validate token %s\n\n", err)
		return
	}

	fmt.Printf("Valid token %s\n\n", tokenString)
}