Reporter @Duecki1 hit "Incorrect Password" on byte-correct input from
Instagram's iOS/Android IAB. Backend bcrypt compare is fine — the
frontend was handing it a mangled byte sequence because the password
Input lacked the autocaps/autocorrect/spellcheck/autocomplete defenses
Instagram's WKWebView keyboard bridge needs (the standard `type="password"`
WebKit defaults that suppress autocaps get overridden inside the IAB).
Three layers of defense:
1. **Explicit input attributes** on the gallery password field —
`autoCapitalize="none"`, `autoCorrect="off"`, `spellCheck={false}`,
`autoComplete="current-password"`. Stops iOS autocaps turning
`wedding2026` into `Wedding2026`, stops predictive-text rewrites,
nudges password managers to autofill the right credential rather
than the IAB's stale saved-password store.
2. **Silent `.trim()` on submit** — Android Instagram IAB's predictive
keyboard often appends a trailing space when the user taps the
submit button. Event-gallery passwords don't legitimately carry
leading/trailing whitespace (they're set by photographers, usually
generated short strings), so trimming here is safe.
3. **Instagram IAB detection banner** — `frontend/src/utils/inAppBrowser.ts`
detects the `Instagram` UA tag and surfaces a one-time advisory at
the top of the password card with the right platform-specific
"Open in external browser" instructions (⋯ menu copy for iOS,
⋮ for Android). Self-rescue path for users who hit it before we
can close every keyboard mangling vector.
Scope is strictly Instagram per #654. Facebook IAB (`FBAV`/`FBAN`)
behaves identically and would benefit, but expanding the matcher is
a separate scope decision — the detector + i18n shape leaves room for
it without further refactor.
EN + DE i18n for the banner; 8 vitest cases on `detectInAppBrowser`
(iOS / Android Instagram UAs, plain Safari / Chrome / desktop UAs,
case-insensitive match, word-boundary defense against substring
collisions, SSR-safety when `navigator` is undefined). Lint + tsc
clean; pre-push Playwright smoke still expected green.
Closes#654.
Paul Nothaft
b1bfd4838e