jwt example

package main

import (
    "fmt"
    "os"
    "time"

    "github.com/golang-jwt/jwt/v5"
)

type CustomClaim struct {
    Id string `json:"id"`
    jwt.RegisteredClaims
}

func generateToken(id string) string {
    key, err := os.ReadFile("./app.rsa")
    if err != nil {
        panic(err)
    }

    private_key, err := jwt.ParseRSAPrivateKeyFromPEM(key)
    if err != nil {
        panic(err)
    }

    claim := CustomClaim{
        Id: id,
        RegisteredClaims: jwt.RegisteredClaims{
            IssuedAt:  jwt.NewNumericDate(time.Now()),
            ExpiresAt: jwt.NewNumericDate(time.Now().Add(time.Hour * 24)),
        },
    }

    token := jwt.NewWithClaims(jwt.SigningMethodRS256, &claim)

    ss, err := token.SignedString(private_key)
    if err != nil {
        panic(err)
    }

    return string(ss)
}

func ParseJwt(token string) CustomClaim {
    key, err := os.ReadFile("./app.rsa.pub")
    if err != nil {
        panic(err)
    }

    pub_key, err := jwt.ParseRSAPublicKeyFromPEM(key)

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

        return pub_key, nil
    })

    if err != nil {
        panic(err)
    }

    if parsed, ok := claim.Claims.(*CustomClaim); ok {
        return *parsed
    }

    panic("failed parsed")
}

func main() {
    token := generateToken("foo")

    fmt.Println(token)

    parsed := ParseJwt(token)

    fmt.Println("jwt id: ", parsed.ID)
    fmt.Println("issued at: ", parsed.IssuedAt)
}