// Vikunja is a to-do list application to facilitate your life.
// Copyright 2018-present Vikunja and contributors. All rights reserved.
//
// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU Affero General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU Affero General Public License for more details.
//
// You should have received a copy of the GNU Affero General Public License
// along with this program.  If not, see <https://www.gnu.org/licenses/>.

package oauth2server

import (
	"crypto/sha256"
	"encoding/base64"
)

// VerifyPKCE verifies a PKCE code_verifier against a stored code_challenge using S256.
// S256: BASE64URL(SHA256(code_verifier)) == code_challenge
func VerifyPKCE(codeVerifier, codeChallenge, codeChallengeMethod string) bool {
	if codeChallengeMethod != "S256" {
		return false
	}

	h := sha256.Sum256([]byte(codeVerifier))
	computed := base64.RawURLEncoding.EncodeToString(h[:])
	return computed == codeChallenge
}