decoding JWT in GO experiment

jwtdecode.go

package jwtdecode

import (
	"encoding/base64"
	"strings"
)

type JWTBlob struct {
	RawJWT string
}

func (j JWTBlob) Parts() []string {
	return strings.Split(j.RawJWT, ".")
}

func (j JWTBlob) PayloadPart() string {
	return j.Parts()[1]
}

// shamelessly stolen from https://github.com/dgrijalva/jwt-go/blob/06ea1031745cb8b3dab3f6a236daf2b0aa468b7e/token.go#L102
func (j JWTBlob) DecodedPayloadPart() ([]byte, error) {
	seg := j.PayloadPart()
	if l := len(seg) % 4; l > 0 {
		seg += strings.Repeat("=", 4-l)
	}

	return base64.URLEncoding.DecodeString(seg)
}

jwtdecode_test.go

package jwtdecode

import (
	"testing"

	"github.com/stretchr/testify/assert"
)

const (
	jwt_example_a = "eyJ0eXAiOiJKV1QiLCJhbGciOiJIUzI1NiJ9.eyJ1c2VySWQiOiJiMDhmODZhZi0zNWRhLTQ4ZjItOGZhYi1jZWYzOTA0NjYwYmQifQ.-xN_h82PHVTCMA9vdoHrcZxH-x5mb11y1537t3rGzcM"
)

func TestParts(t *testing.T) {
	assert := assert.New(t)
	jwtblob := JWTBlob{RawJWT: jwt_example_a}
	actual_parts := jwtblob.Parts()
	expected_parts := []string{
		"eyJ0eXAiOiJKV1QiLCJhbGciOiJIUzI1NiJ9",
		"eyJ1c2VySWQiOiJiMDhmODZhZi0zNWRhLTQ4ZjItOGZhYi1jZWYzOTA0NjYwYmQifQ",
		"-xN_h82PHVTCMA9vdoHrcZxH-x5mb11y1537t3rGzcM",
	}
	assert.Equal(expected_parts, actual_parts, "should be equal")
}

func TestPayloadPart(t *testing.T) {
	assert := assert.New(t)
	jwtblob := JWTBlob{RawJWT: jwt_example_a}
	actual_payload_part := jwtblob.PayloadPart()
	expected_payload_part := "eyJ1c2VySWQiOiJiMDhmODZhZi0zNWRhLTQ4ZjItOGZhYi1jZWYzOTA0NjYwYmQifQ"
	assert.Equal(expected_payload_part, actual_payload_part)
}

func TestDecodedPayloadPart(t *testing.T) {
	assert := assert.New(t)
	jwtblob := JWTBlob{RawJWT: jwt_example_a}
	actual_decoded_payload, _ := jwtblob.DecodedPayloadPart()
	expected_decoded_payload := `{"userId":"b08f86af-35da-48f2-8fab-cef3904660bd"}`
	assert.Equal(expected_decoded_payload, string(actual_decoded_payload))
}