Kwaku Danso
dbddf17e3b
When a guest submitted via their invitation and then forwarded the link
(or someone copied the URL), the recipient was shown the original guest's
response and a "Change my response" button. Two real problems:
- Privacy leak: the original guest's reply was visible
- Integrity: the recipient could silently overwrite the response
The fix is two layered defences plus a recovery path, matching the
industry pattern used by Eventbrite / Partiful / Lu.ma:
Backend
- GET /access/{token} now compares the device fingerprint of the
current request to the fingerprint stored on the existing RSVP.
When they don't match, the rsvp field is omitted from the
response and a new rsvp_submitted_elsewhere flag is set instead.
The original guest's reply stays private.
- PATCH /rsvp/{token} runs the same gate before scoring. A foreign
device gets 403 with a hint to request an edit link.
- The fingerprint check is intentionally narrow (user_agent only),
so a guest jumping between Wi-Fi and mobile data on the same
phone still sails through.
Recovery path
- New POST /access/{token}/request-edit-link mints a short-lived
edit nonce (Redis, 30-min TTL, SHA-256-hashed), then emails it
to the guest's address on file via the existing EmailSender.
Rate-limited to 3 per token per hour.
- GET /access/{token}?edit=<nonce> and PATCH /rsvp with edit_nonce
in the body both accept the nonce as a bypass for the
same-device check. Lets the real guest edit from a new phone
when their original device is gone.
- New SendRSVPEditLink method on auth.EmailSender, implemented by
every concrete sender (log stub / Resend / SMTP / SES), with a
branded HTML+text template that explains the "we sent this
because we didn't recognise the device" framing.
Frontend
- rsvp/[token].vue learns the new "responded elsewhere" state.
Renders "This invitation has already been used" + a
"Send me an edit link" CTA when the access response says we
have somewhere to deliver it. Empty-state copy reads "If you
forwarded the link, please ask the original guest to reach
out to the host".
- When the URL carries ?edit=<nonce>, the page passes it on the
/access call (so the backend unhides the RSVP), opens the edit
form pre-populated, and forwards the nonce on PATCH.
- Removed two leftover leaks from earlier — the page no longer
shows internal "Risk score N · band" to confirmed or blocked
guests; the blocked-attempt copy now reads "Something about
this attempt looked off" rather than "suspicious access
attempt".
Defensive nil-guard
- The access handler's NATS publish goroutine now skips when
deps.AccessPublisher is nil (matches the rsvp publisher's
existing guard); without it the handler nil-panicked in tests
that don't wire NATS.
Tests
- TestFingerprintsSimilar (unit) covers the same-UA / different-UA
/ missing-UA matrix.
- TestForwardedInvitationLinkDefence (integration) walks the full
flow: submit from UA-A, hide on UA-B, request link, follow nonce
from UA-B and edit, then verify a UA-C with a forged nonce is
still refused.
- Full integration suite passes (183.5s).
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
53 lines
1.4 KiB
Go
53 lines
1.4 KiB
Go
package api
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import "testing"
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func TestFingerprintsSimilar(t *testing.T) {
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const ua = "Mozilla/5.0 (Macintosh; Intel Mac OS X 14_2) AppleWebKit/605"
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other := "Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537"
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tests := []struct {
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name string
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stored, current map[string]any
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want bool
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}{
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{
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name: "identical UA, different IPs counts as same device",
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stored: map[string]any{"user_agent": ua, "accept_language": "en"},
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current: map[string]any{"user_agent": ua, "accept_language": "fr"},
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want: true,
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},
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{
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name: "different UA never matches",
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stored: map[string]any{"user_agent": ua},
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current: map[string]any{"user_agent": other},
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want: false,
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},
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{
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name: "missing UA on current side is treated as mismatch",
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stored: map[string]any{"user_agent": ua},
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current: map[string]any{},
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want: false,
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},
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{
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name: "missing UA on stored side is treated as mismatch",
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stored: map[string]any{},
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current: map[string]any{"user_agent": ua},
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want: false,
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},
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{
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name: "both nil is mismatch (conservative default)",
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stored: nil,
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current: nil,
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want: false,
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},
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}
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for _, tc := range tests {
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t.Run(tc.name, func(t *testing.T) {
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if got := fingerprintsSimilar(tc.stored, tc.current); got != tc.want {
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t.Errorf("fingerprintsSimilar = %v, want %v", got, tc.want)
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}
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})
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}
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}
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