JWT Email Token

token.go

package email

import (
	"crypto/rsa"
	"time"

	jwt "github.com/dgrijalva/jwt-go"
	"github.com/pkg/errors"
)

const (
	tokenExpiresIn = 15000
)

// TokenHandler is the struct that
// generates JWT tokens.
type TokenHandler struct {
	PrivateKey *rsa.PrivateKey
}

// Claims is the struct that represent
// JWT claims according to
// https://tools.ietf.org/html/rfc7519#
// section-4
type Claims struct {
	Email string `json:"email"`
	jwt.StandardClaims
}

// NewToken creates a token for email
// verification with the given subject
// and email.
func (e *TokenHandler) NewToken(
	subject string,
	email string,
) (string, error) {

	createdAt := time.Now().Unix()
	t := jwt.NewWithClaims(
		jwt.SigningMethodRS256,
		Claims{
			StandardClaims: jwt.StandardClaims{
				Subject:   subject,
				ExpiresAt: createdAt + tokenExpiresIn,
				IssuedAt:  createdAt,
				NotBefore: createdAt,
			},
			Email: email,
		})
	return t.SignedString(e.PrivateKey)
}

// Verify validates a given token and
// returns subject and email form it.
func (e TokenHandler) Verify(token string) (
	string,
	string,
	error,
) {
	parsed, err := jwt.ParseWithClaims(
		token, &Claims{},
		func(t *jwt.Token) (interface{}, error) {
			return &e.PrivateKey.PublicKey, nil
		},
	)

	if err != nil {
		return "", "", err
	}

	if claims, ok := parsed.Claims.(*Claims); ok && parsed.Valid {
		return claims.StandardClaims.Subject,
			claims.Email,
			nil
	}
	return "", "", errors.New("invalid token")
}