1 // Copyright 2012 The Go Authors. All rights reserved.
2 // Use of this source code is governed by a BSD-style
3 // license that can be found in the LICENSE file.
5 // Package xsrftoken provides methods for generating and validating secure XSRF tokens.
6 package xsrftoken // import "golang.org/x/net/xsrftoken"
19 // Timeout is the duration for which XSRF tokens are valid.
20 // It is exported so clients may set cookie timeouts that match generated tokens.
21 const Timeout = 24 * time.Hour
23 // clean sanitizes a string for inclusion in a token by replacing all ":"s.
24 func clean(s string) string {
25 return strings.Replace(s, ":", "_", -1)
28 // Generate returns a URL-safe secure XSRF token that expires in 24 hours.
30 // key is a secret key for your application; it must be non-empty.
31 // userID is an optional unique identifier for the user.
32 // actionID is an optional action the user is taking (e.g. POSTing to a particular path).
33 func Generate(key, userID, actionID string) string {
34 return generateTokenAtTime(key, userID, actionID, time.Now())
37 // generateTokenAtTime is like Generate, but returns a token that expires 24 hours from now.
38 func generateTokenAtTime(key, userID, actionID string, now time.Time) string {
40 panic("zero length xsrf secret key")
42 // Round time up and convert to milliseconds.
43 milliTime := (now.UnixNano() + 1e6 - 1) / 1e6
45 h := hmac.New(sha1.New, []byte(key))
46 fmt.Fprintf(h, "%s:%s:%d", clean(userID), clean(actionID), milliTime)
48 // Get the padded base64 string then removing the padding.
49 tok := string(h.Sum(nil))
50 tok = base64.URLEncoding.EncodeToString([]byte(tok))
51 tok = strings.TrimRight(tok, "=")
53 return fmt.Sprintf("%s:%d", tok, milliTime)
56 // Valid reports whether a token is a valid, unexpired token returned by Generate.
57 func Valid(token, key, userID, actionID string) bool {
58 return validTokenAtTime(token, key, userID, actionID, time.Now())
61 // validTokenAtTime reports whether a token is valid at the given time.
62 func validTokenAtTime(token, key, userID, actionID string, now time.Time) bool {
64 panic("zero length xsrf secret key")
66 // Extract the issue time of the token.
67 sep := strings.LastIndex(token, ":")
71 millis, err := strconv.ParseInt(token[sep+1:], 10, 64)
75 issueTime := time.Unix(0, millis*1e6)
77 // Check that the token is not expired.
78 if now.Sub(issueTime) >= Timeout {
82 // Check that the token is not from the future.
83 // Allow 1 minute grace period in case the token is being verified on a
84 // machine whose clock is behind the machine that issued the token.
85 if issueTime.After(now.Add(1 * time.Minute)) {
89 expected := generateTokenAtTime(key, userID, actionID, issueTime)
91 // Check that the token matches the expected value.
92 // Use constant time comparison to avoid timing attacks.
93 return subtle.ConstantTimeCompare([]byte(token), []byte(expected)) == 1