sulthan
7d0eaaef02
Adds sessionKey/signSession/verifySession primitives and setSessionCookie/clearSessionCookie helpers in a new backend/session.go. Sessions are derived from API_TOKEN via HMAC-SHA256 with domain separation (sessionKeyPurpose), so there is no session table and rotating the token invalidates every outstanding cookie at once. No routes or handlers yet — that's task 5.
90 lines
2.7 KiB
Go
90 lines
2.7 KiB
Go
package main
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import (
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"crypto/hmac"
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"crypto/sha256"
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"crypto/subtle"
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"encoding/base64"
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"net/http"
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"strconv"
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"strings"
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"time"
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)
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const (
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sessionCookieName = "mangabm_session"
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// 60 days: long enough that a phone stays logged in between reading spells.
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sessionTTL = 60 * 24 * time.Hour
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// Domain separation, so the session key can never collide with any other
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// use of API_TOKEN. Changing this string logs everyone out.
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sessionKeyPurpose = "mangabm-web-session-v1"
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)
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// sessionKey derives the cookie-signing key from the API token. Sessions are
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// stateless — there is no session table — so rotating API_TOKEN invalidates
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// every outstanding cookie at once.
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func sessionKey(apiToken string) []byte {
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sum := sha256.Sum256([]byte(apiToken + sessionKeyPurpose))
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return sum[:]
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}
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// signSession encodes "<expiryMs>.<base64url HMAC(expiryMs)>".
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func signSession(key []byte, expiryMs int64) string {
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payload := strconv.FormatInt(expiryMs, 10)
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return payload + "." + sessionMAC(key, payload)
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}
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func sessionMAC(key []byte, payload string) string {
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mac := hmac.New(sha256.New, key)
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mac.Write([]byte(payload))
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return base64.RawURLEncoding.EncodeToString(mac.Sum(nil))
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}
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// verifySession checks shape, then expiry, then the signature — in that order.
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// The signature comparison is constant-time; the checks before it only look at
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// data the holder already supplied, so their timing leaks nothing.
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func verifySession(key []byte, value string, nowMs int64) bool {
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payload, sig, ok := strings.Cut(value, ".")
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if !ok {
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return false
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}
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expiry, err := strconv.ParseInt(payload, 10, 64)
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if err != nil || expiry <= nowMs {
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return false
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}
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want := sessionMAC(key, payload)
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return subtle.ConstantTimeCompare([]byte(sig), []byte(want)) == 1
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}
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// isHTTPS reports whether the browser's connection is encrypted. Behind Traefik
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// the Go server itself speaks plain HTTP, so the forwarded header is the only
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// signal; without this check the Secure cookie would never be set in
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// production, and setting it unconditionally would break http://localhost dev.
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func isHTTPS(r *http.Request) bool {
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return r.TLS != nil || r.Header.Get("X-Forwarded-Proto") == "https"
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}
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func setSessionCookie(w http.ResponseWriter, r *http.Request, key []byte) {
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http.SetCookie(w, &http.Cookie{
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Name: sessionCookieName,
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Value: signSession(key, time.Now().Add(sessionTTL).UnixMilli()),
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Path: "/",
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MaxAge: int(sessionTTL / time.Second),
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HttpOnly: true,
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Secure: isHTTPS(r),
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SameSite: http.SameSiteLaxMode,
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})
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}
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func clearSessionCookie(w http.ResponseWriter, r *http.Request) {
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http.SetCookie(w, &http.Cookie{
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Name: sessionCookieName,
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Value: "",
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Path: "/",
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MaxAge: -1,
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HttpOnly: true,
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Secure: isHTTPS(r),
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SameSite: http.SameSiteLaxMode,
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})
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}
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