uncensored-send/internal/server/login.go

package server

import (
	"net/http"
	"net/url"
	"strings"

	"uncensored-send/internal/config"
)

// loginPage backs both the form and its error redisplay.
type loginPage struct {
	page
	Error string
	Next  string

	// Limits describe what the presented credential would be allowed to do,
	// shown once logged in so the upload page does not have to guess.
	MaxSize   string
	MaxExpiry string
	Vanity    bool
}

// loginDestinations is the allowlist for the post-login redirect. Restricting
// it to known page names means the parameter can never name somewhere else.
var loginDestinations = map[string]string{
	"":      "",
	"admin": "admin",
}

func destination(next string) string {
	page, ok := loginDestinations[next]
	if !ok {
		return ""
	}
	return page
}

func (s *Server) handleLoginPage(w http.ResponseWriter, r *http.Request) {
	next := destination(r.URL.Query().Get("next"))

	// Already logged in: say so rather than showing an empty form.
	if lim, err := s.limitsFor(r, cookieCredential(r)); err == nil && !lim.Anonymous() {
		s.render(w, http.StatusOK, "login.html", loginPage{
			page:      s.page(r, "Log in", false),
			Next:      next,
			MaxSize:   config.FormatSize(lim.MaxSize),
			MaxExpiry: config.FormatLifetime(lim.MaxExpiry),
			Vanity:    lim.AllowVanity,
		})
		return
	}
	s.render(w, http.StatusOK, "login.html", loginPage{
		page: s.page(r, "Log in", false),
		Next: next,
	})
}

func (s *Server) handleLogin(w http.ResponseWriter, r *http.Request) {
	r.Body = http.MaxBytesReader(w, r.Body, maxFieldBytes)
	if err := r.ParseForm(); err != nil {
		s.fail(w, r, http.StatusBadRequest, "Malformed form submission.")
		return
	}
	token := strings.TrimSpace(r.PostFormValue("token"))
	next := destination(r.PostFormValue("next"))

	if token == "" {
		s.loginFailed(w, r, next, http.StatusBadRequest, "Enter a token.")
		return
	}
	// Only failures are throttled, so logging in normally is never delayed.
	lim, err := s.limitsFor(r, token)
	if err != nil {
		if !s.authLimiter.allow(clientIP(r, s.cfg), s.now()) {
			s.loginFailed(w, r, next, http.StatusTooManyRequests,
				"Too many failed attempts; try again shortly.")
			return
		}
		s.log.Info("failed login", "ip", clientIP(r, s.cfg))
		s.loginFailed(w, r, next, http.StatusUnauthorized, "That token is not recognised.")
		return
	}

	s.logIn(w, r, token, r.PostFormValue("persist") != "")
	s.log.Info("logged in", "name", lim.Name, "ip", clientIP(r, s.cfg))

	if wantsJSON(r) {
		writeJSON(w, http.StatusOK, map[string]string{"status": "logged in", "name": lim.Name})
		return
	}
	http.Redirect(w, r, s.cfg.BasePath+next, http.StatusSeeOther)
}

func (s *Server) loginFailed(w http.ResponseWriter, r *http.Request, next string, status int, msg string) {
	if wantsJSON(r) {
		s.fail(w, r, status, msg)
		return
	}
	s.render(w, status, "login.html", loginPage{
		page:  s.page(r, "Log in", false),
		Error: msg,
		Next:  next,
	})
}

func (s *Server) handleLogout(w http.ResponseWriter, r *http.Request) {
	s.forget(w, r)
	if wantsJSON(r) {
		writeJSON(w, http.StatusOK, map[string]string{"status": "logged out"})
		return
	}
	http.Redirect(w, r, s.cfg.BasePath, http.StatusSeeOther)
}

// sameOrigin guards the state-changing routes against cross-site form posts.
//
// The cookie is SameSite=Strict, which already stops another site from acting
// as a logged-in user. This covers the case that does not need a cookie at all:
// a hostile page posting to /login to sign a visitor into an account the
// attacker controls, so that the visitor's uploads land under it.
//
// Browsers label their own requests; API clients send neither header, and their
// bearer tokens are not attachable by a third party anyway. So an absent label
// is allowed and a present one must say same-origin.
func sameOrigin(r *http.Request) bool {
	switch r.Header.Get("Sec-Fetch-Site") {
	case "same-origin", "none":
		return true
	case "": // older browser, or not a browser at all; fall through to Origin
	default:
		return false
	}

	origin := r.Header.Get("Origin")
	if origin == "" || origin == "null" {
		return origin == ""
	}
	u, err := url.Parse(origin)
	if err != nil {
		return false
	}
	return u.Host == r.Host
}

func (s *Server) requireSameOrigin(next http.Handler) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		if r.Method == http.MethodPost && !sameOrigin(r) {
			s.log.Info("rejected cross-origin post", "path", r.URL.Path,
				"origin", r.Header.Get("Origin"), "ip", clientIP(r, s.cfg))
			s.fail(w, r, http.StatusForbidden, "Cross-site form submissions are not accepted.")
			return
		}
		next.ServeHTTP(w, r)
	})
}