95 lines
3 KiB
Go
95 lines
3 KiB
Go
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// Copyright 2012 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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// Package xsrftoken provides methods for generating and validating secure XSRF tokens.
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package xsrftoken // import "golang.org/x/net/xsrftoken"
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import (
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"crypto/hmac"
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"crypto/sha1"
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"crypto/subtle"
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"encoding/base64"
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"fmt"
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"strconv"
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"strings"
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"time"
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)
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// Timeout is the duration for which XSRF tokens are valid.
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// It is exported so clients may set cookie timeouts that match generated tokens.
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const Timeout = 24 * time.Hour
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// clean sanitizes a string for inclusion in a token by replacing all ":"s.
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func clean(s string) string {
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return strings.Replace(s, ":", "_", -1)
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}
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// Generate returns a URL-safe secure XSRF token that expires in 24 hours.
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//
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// key is a secret key for your application; it must be non-empty.
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// userID is an optional unique identifier for the user.
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// actionID is an optional action the user is taking (e.g. POSTing to a particular path).
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func Generate(key, userID, actionID string) string {
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return generateTokenAtTime(key, userID, actionID, time.Now())
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}
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// generateTokenAtTime is like Generate, but returns a token that expires 24 hours from now.
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func generateTokenAtTime(key, userID, actionID string, now time.Time) string {
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if len(key) == 0 {
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panic("zero length xsrf secret key")
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}
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// Round time up and convert to milliseconds.
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milliTime := (now.UnixNano() + 1e6 - 1) / 1e6
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h := hmac.New(sha1.New, []byte(key))
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fmt.Fprintf(h, "%s:%s:%d", clean(userID), clean(actionID), milliTime)
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// Get the padded base64 string then removing the padding.
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tok := string(h.Sum(nil))
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tok = base64.URLEncoding.EncodeToString([]byte(tok))
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tok = strings.TrimRight(tok, "=")
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return fmt.Sprintf("%s:%d", tok, milliTime)
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}
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// Valid reports whether a token is a valid, unexpired token returned by Generate.
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func Valid(token, key, userID, actionID string) bool {
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return validTokenAtTime(token, key, userID, actionID, time.Now())
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}
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// validTokenAtTime reports whether a token is valid at the given time.
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func validTokenAtTime(token, key, userID, actionID string, now time.Time) bool {
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if len(key) == 0 {
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panic("zero length xsrf secret key")
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}
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// Extract the issue time of the token.
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sep := strings.LastIndex(token, ":")
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if sep < 0 {
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return false
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}
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millis, err := strconv.ParseInt(token[sep+1:], 10, 64)
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if err != nil {
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return false
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}
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issueTime := time.Unix(0, millis*1e6)
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// Check that the token is not expired.
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if now.Sub(issueTime) >= Timeout {
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return false
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}
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// Check that the token is not from the future.
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// Allow 1 minute grace period in case the token is being verified on a
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// machine whose clock is behind the machine that issued the token.
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if issueTime.After(now.Add(1 * time.Minute)) {
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return false
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}
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expected := generateTokenAtTime(key, userID, actionID, issueTime)
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// Check that the token matches the expected value.
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// Use constant time comparison to avoid timing attacks.
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return subtle.ConstantTimeCompare([]byte(token), []byte(expected)) == 1
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}
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