verifier.go

package go_oauth_pkce_code_verifier

import (
	"crypto/sha256"
	"encoding/base64"
	"fmt"
	"math/rand"
	"strings"
	"time"
)

const (
	DefaultLength = 32
	MinLength     = 32
	MaxLength     = 96
)

type CodeVerifier struct {
	Value string
}

func CreateCodeVerifier() (*CodeVerifier, error) {
	return CreateCodeVerifierWithLength(DefaultLength)
}

func CreateCodeVerifierWithLength(length int) (*CodeVerifier, error) {
	if length < MinLength || length > MaxLength {
		return nil, fmt.Errorf("invalid length: %v", length)
	}
	r := rand.New(rand.NewSource(time.Now().UnixNano()))
	b := make([]byte, length, length)
	for i := 0; i < length; i++ {
		b[i] = byte(r.Intn(255))
	}
	return CreateCodeVerifierFromBytes(b)
}

func CreateCodeVerifierFromBytes(b []byte) (*CodeVerifier, error) {
	return &CodeVerifier{
		Value: encode(b),
	}, nil
}

func (v *CodeVerifier) String() string {
	return v.Value
}

func (v *CodeVerifier) CodeChallengePlain() string {
	return v.Value
}

func (v *CodeVerifier) CodeChallengeS256() string {
	h := sha256.New()
	h.Write([]byte(v.Value))
	return encode(h.Sum(nil))
}

func encode(msg []byte) string {
	encoded := base64.StdEncoding.EncodeToString(msg)
	encoded = strings.Replace(encoded, "+", "-", -1)
	encoded = strings.Replace(encoded, "/", "_", -1)
	encoded = strings.Replace(encoded, "=", "", -1)
	return encoded
}