fix: make pkce code_verifier spec compliant #125

follow recommendations for code_verifier: https://datatracker.ietf.org/doc/html/rfc7636#section-4.1

pkg/client/rp/relaying_party.go

@@ -2,6 +2,7 @@ package rp
 
 import (
 	"context"
+	"encoding/base64"
 	"errors"
 	"net/http"
 	"strings"
@@ -288,7 +289,7 @@ func AuthURLHandler(stateFn func() string, rp RelyingParty) http.HandlerFunc {
 
 //GenerateAndStoreCodeChallenge generates a PKCE code challenge and stores its verifier into a secure cookie
 func GenerateAndStoreCodeChallenge(w http.ResponseWriter, rp RelyingParty) (string, error) {
-	codeVerifier := uuid.New().String()
+	codeVerifier := base64.URLEncoding.EncodeToString([]byte(uuid.New().String()))
 	if err := rp.CookieHandler().SetCookie(w, pkceCode, codeVerifier); err != nil {
 		return "", err
 	}