gophertype/pkg/middleware/csrf.go

package middleware

import (
	"context"
	"net/http"

	"git.kirsle.net/apps/gophertype/pkg/constants"
	"git.kirsle.net/apps/gophertype/pkg/responses"
	"git.kirsle.net/apps/gophertype/pkg/session"
	uuid "github.com/satori/go.uuid"
)

// CSRF prevents Cross-Site Request Forgery.
// All "POST" requests are required to have an "_csrf" variable passed in which
// matches the "csrf_token" HTTP cookie with their request.
func CSRF(next http.Handler) http.Handler {
	middleware := func(w http.ResponseWriter, r *http.Request) {
		// All requests: verify they have a CSRF cookie, create one if not.
		var token string
		cookie, err := r.Cookie(constants.CSRFCookieName)
		if err == nil {
			token = cookie.Value
		}

		// Generate a token cookie if not found.
		if len(token) < 8 || err != nil {
			token = uuid.NewV4().String()
			cookie = &http.Cookie{
				Name:  constants.CSRFCookieName,
				Value: token,
			}
			http.SetCookie(w, cookie)
		}

		// Add the CSRF token to the request context. This makes it immediately
		// available on FIRST page load, when the cookie hasn't been sent back
		// from the browser yet.
		ctx := context.WithValue(r.Context(), session.CSRFKey, token)

		// POST requests: verify token from form parameter.
		if r.Method == http.MethodPost {
			compare := r.FormValue(constants.CSRFFormName)
			if compare != token {
				responses.Panic(w, http.StatusForbidden, "CSRF token failure.")
				return
			}
		}

		next.ServeHTTP(w, r.WithContext(ctx))
	}

	return http.HandlerFunc(middleware)
}