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package csrf
import (
"net/http"
"time"
"github.com/gorilla/securecookie"
)
// store represents the session storage used for CSRF tokens.
type store interface {
// Get returns the real CSRF token from the store.
Get(*http.Request) ([]byte, error)
// Save stores the real CSRF token in the store and writes a
// cookie to the http.ResponseWriter.
// For non-cookie stores, the cookie should contain a unique (256 bit) ID
// or key that references the token in the backend store.
// csrf.GenerateRandomBytes is a helper function for generating secure IDs.
Save(token []byte, w http.ResponseWriter) error
}
// cookieStore is a signed cookie session store for CSRF tokens.
type cookieStore struct {
name string
maxAge int
secure bool
httpOnly bool
path string
domain string
sc *securecookie.SecureCookie
}
// Get retrieves a CSRF token from the session cookie. It returns an empty token
// if decoding fails (e.g. HMAC validation fails or the named cookie doesn't exist).
func (cs *cookieStore) Get(r *http.Request) ([]byte, error) {
// Retrieve the cookie from the request
cookie, err := r.Cookie(cs.name)
if err != nil {
return nil, err
}
token := make([]byte, tokenLength)
// Decode the HMAC authenticated cookie.
err = cs.sc.Decode(cs.name, cookie.Value, &token)
if err != nil {
return nil, err
}
return token, nil
}
// Save stores the CSRF token in the session cookie.
func (cs *cookieStore) Save(token []byte, w http.ResponseWriter) error {
// Generate an encoded cookie value with the CSRF token.
encoded, err := cs.sc.Encode(cs.name, token)
if err != nil {
return err
}
cookie := &http.Cookie{
Name: cs.name,
Value: encoded,
MaxAge: cs.maxAge,
HttpOnly: cs.httpOnly,
Secure: cs.secure,
Path: cs.path,
Domain: cs.domain,
}
// Set the Expires field on the cookie based on the MaxAge
// If MaxAge <= 0, we don't set the Expires attribute, making the cookie
// session-only.
if cs.maxAge > 0 {
cookie.Expires = time.Now().Add(
time.Duration(cs.maxAge) * time.Second)
}
// Write the authenticated cookie to the response.
http.SetCookie(w, cookie)
return nil
}
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