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4f3080c Feb 21, 2018
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@vishr @im-kulikov
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package middleware
import (
"crypto/subtle"
"errors"
"net/http"
"strings"
"time"
"github.com/labstack/echo"
"github.com/labstack/gommon/random"
)
type (
// CSRFConfig defines the config for CSRF middleware.
CSRFConfig struct {
// Skipper defines a function to skip middleware.
Skipper Skipper
// TokenLength is the length of the generated token.
TokenLength uint8 `yaml:"token_length"`
// Optional. Default value 32.
// TokenLookup is a string in the form of "<source>:<key>" that is used
// to extract token from the request.
// Optional. Default value "header:X-CSRF-Token".
// Possible values:
// - "header:<name>"
// - "form:<name>"
// - "query:<name>"
TokenLookup string `yaml:"token_lookup"`
// Context key to store generated CSRF token into context.
// Optional. Default value "csrf".
ContextKey string `yaml:"context_key"`
// Name of the CSRF cookie. This cookie will store CSRF token.
// Optional. Default value "csrf".
CookieName string `yaml:"cookie_name"`
// Domain of the CSRF cookie.
// Optional. Default value none.
CookieDomain string `yaml:"cookie_domain"`
// Path of the CSRF cookie.
// Optional. Default value none.
CookiePath string `yaml:"cookie_path"`
// Max age (in seconds) of the CSRF cookie.
// Optional. Default value 86400 (24hr).
CookieMaxAge int `yaml:"cookie_max_age"`
// Indicates if CSRF cookie is secure.
// Optional. Default value false.
CookieSecure bool `yaml:"cookie_secure"`
// Indicates if CSRF cookie is HTTP only.
// Optional. Default value false.
CookieHTTPOnly bool `yaml:"cookie_http_only"`
}
// csrfTokenExtractor defines a function that takes `echo.Context` and returns
// either a token or an error.
csrfTokenExtractor func(echo.Context) (string, error)
)
var (
// DefaultCSRFConfig is the default CSRF middleware config.
DefaultCSRFConfig = CSRFConfig{
Skipper: DefaultSkipper,
TokenLength: 32,
TokenLookup: "header:" + echo.HeaderXCSRFToken,
ContextKey: "csrf",
CookieName: "_csrf",
CookieMaxAge: 86400,
}
)
// CSRF returns a Cross-Site Request Forgery (CSRF) middleware.
// See: https://en.wikipedia.org/wiki/Cross-site_request_forgery
func CSRF() echo.MiddlewareFunc {
c := DefaultCSRFConfig
return CSRFWithConfig(c)
}
// CSRFWithConfig returns a CSRF middleware with config.
// See `CSRF()`.
func CSRFWithConfig(config CSRFConfig) echo.MiddlewareFunc {
// Defaults
if config.Skipper == nil {
config.Skipper = DefaultCSRFConfig.Skipper
}
if config.TokenLength == 0 {
config.TokenLength = DefaultCSRFConfig.TokenLength
}
if config.TokenLookup == "" {
config.TokenLookup = DefaultCSRFConfig.TokenLookup
}
if config.ContextKey == "" {
config.ContextKey = DefaultCSRFConfig.ContextKey
}
if config.CookieName == "" {
config.CookieName = DefaultCSRFConfig.CookieName
}
if config.CookieMaxAge == 0 {
config.CookieMaxAge = DefaultCSRFConfig.CookieMaxAge
}
// Initialize
parts := strings.Split(config.TokenLookup, ":")
extractor := csrfTokenFromHeader(parts[1])
switch parts[0] {
case "form":
extractor = csrfTokenFromForm(parts[1])
case "query":
extractor = csrfTokenFromQuery(parts[1])
}
return func(next echo.HandlerFunc) echo.HandlerFunc {
return func(c echo.Context) error {
if config.Skipper(c) {
return next(c)
}
req := c.Request()
k, err := c.Cookie(config.CookieName)
token := ""
// Generate token
if err != nil {
token = random.String(config.TokenLength)
} else {
// Reuse token
token = k.Value
}
switch req.Method {
case echo.GET, echo.HEAD, echo.OPTIONS, echo.TRACE:
default:
// Validate token only for requests which are not defined as 'safe' by RFC7231
clientToken, err := extractor(c)
if err != nil {
return echo.NewHTTPError(http.StatusBadRequest, err.Error())
}
if !validateCSRFToken(token, clientToken) {
return echo.NewHTTPError(http.StatusForbidden, "invalid csrf token")
}
}
// Set CSRF cookie
cookie := new(http.Cookie)
cookie.Name = config.CookieName
cookie.Value = token
if config.CookiePath != "" {
cookie.Path = config.CookiePath
}
if config.CookieDomain != "" {
cookie.Domain = config.CookieDomain
}
cookie.Expires = time.Now().Add(time.Duration(config.CookieMaxAge) * time.Second)
cookie.Secure = config.CookieSecure
cookie.HttpOnly = config.CookieHTTPOnly
c.SetCookie(cookie)
// Store token in the context
c.Set(config.ContextKey, token)
// Protect clients from caching the response
c.Response().Header().Add(echo.HeaderVary, echo.HeaderCookie)
return next(c)
}
}
}
// csrfTokenFromForm returns a `csrfTokenExtractor` that extracts token from the
// provided request header.
func csrfTokenFromHeader(header string) csrfTokenExtractor {
return func(c echo.Context) (string, error) {
return c.Request().Header.Get(header), nil
}
}
// csrfTokenFromForm returns a `csrfTokenExtractor` that extracts token from the
// provided form parameter.
func csrfTokenFromForm(param string) csrfTokenExtractor {
return func(c echo.Context) (string, error) {
token := c.FormValue(param)
if token == "" {
return "", errors.New("missing csrf token in the form parameter")
}
return token, nil
}
}
// csrfTokenFromQuery returns a `csrfTokenExtractor` that extracts token from the
// provided query parameter.
func csrfTokenFromQuery(param string) csrfTokenExtractor {
return func(c echo.Context) (string, error) {
token := c.QueryParam(param)
if token == "" {
return "", errors.New("missing csrf token in the query string")
}
return token, nil
}
}
func validateCSRFToken(token, clientToken string) bool {
return subtle.ConstantTimeCompare([]byte(token), []byte(clientToken)) == 1
}