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// Copyright 2012 Google Inc. All Rights Reserved.
// Copyright 2014 The Macaron Authors
// Copyright 2020 The Gitea Authors
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package context
import (
"bytes"
"crypto/hmac"
"crypto/sha1"
"crypto/subtle"
"encoding/base64"
"fmt"
"strconv"
"strings"
"time"
)
// Timeout represents the duration that XSRF tokens are valid.
// It is exported so clients may set cookie timeouts that match generated tokens.
const Timeout = 24 * time.Hour
// clean sanitizes a string for inclusion in a token by replacing all ":"s.
func clean(s string) string {
return strings.ReplaceAll(s, ":", "_")
}
// GenerateToken returns a URL-safe secure XSRF token that expires in 24 hours.
//
// key is a secret key for your application.
// userID is a unique identifier for the user.
// actionID is the action the user is taking (e.g. POSTing to a particular path).
func GenerateToken(key, userID, actionID string) string {
return generateTokenAtTime(key, userID, actionID, time.Now())
}
// generateTokenAtTime is like Generate, but returns a token that expires 24 hours from now.
func generateTokenAtTime(key, userID, actionID string, now time.Time) string {
h := hmac.New(sha1.New, []byte(key))
fmt.Fprintf(h, "%s:%s:%d", clean(userID), clean(actionID), now.UnixNano())
tok := fmt.Sprintf("%s:%d", h.Sum(nil), now.UnixNano())
return base64.RawURLEncoding.EncodeToString([]byte(tok))
}
// ValidToken returns true if token is a valid, unexpired token returned by Generate.
func ValidToken(token, key, userID, actionID string) bool {
return validTokenAtTime(token, key, userID, actionID, time.Now())
}
// validTokenAtTime is like Valid, but it uses now to check if the token is expired.
func validTokenAtTime(token, key, userID, actionID string, now time.Time) bool {
// Decode the token.
data, err := base64.RawURLEncoding.DecodeString(token)
if err != nil {
return false
}
// Extract the issue time of the token.
sep := bytes.LastIndex(data, []byte{':'})
if sep < 0 {
return false
}
nanos, err := strconv.ParseInt(string(data[sep+1:]), 10, 64)
if err != nil {
return false
}
issueTime := time.Unix(0, nanos)
// Check that the token is not expired.
if now.Sub(issueTime) >= Timeout {
return false
}
// Check that the token is not from the future.
// Allow 1 minute grace period in case the token is being verified on a
// machine whose clock is behind the machine that issued the token.
if issueTime.After(now.Add(1 * time.Minute)) {
return false
}
expected := generateTokenAtTime(key, userID, actionID, issueTime)
// Check that the token matches the expected value.
// Use constant time comparison to avoid timing attacks.
return subtle.ConstantTimeCompare([]byte(token), []byte(expected)) == 1
}
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