F109: When Split Fields Force a Cognitive Test

A six-digit code. Six separate input boxes. Paste blocked. For the compliance officer reviewing their organization's authentication flows right now, this pattern probably looks familiar — and it may be sitting in your login stack as a documented WCAG 2.2 failure.

WCAG Failure F109 (opens in new window) describes exactly this scenario. It's an official entry in W3C's technique catalog documenting a specific pattern that fails Success Criterion 3.3.8 Accessible Authentication (Minimum) (opens in new window) and SC 3.3.9 Accessible Authentication (Enhanced) (opens in new window). The thesis of F109 is straightforward: requiring users to authenticate by entering a password or code in a different format from which it was originally created — without offering an alternative — is a failure. Not a gray area. A documented failure.

The Failure Pattern

F109 catalogs three concrete failure patterns. Each one shares the same structural problem: the interface fragments a credential into pieces that cannot be entered as a single, pasteable string.

Pattern 1 — Split TOTP fields:

<!-- FAILURE: Each digit in a separate input, paste blocked -->
<fieldset>
  <legend>Enter your 6-digit verification code</legend>
  <input type="text" maxlength="1" aria-label="Digit 1">
  <input type="text" maxlength="1" aria-label="Digit 2">
  <input type="text" maxlength="1" aria-label="Digit 3">
  <input type="text" maxlength="1" aria-label="Digit 4">
  <input type="text" maxlength="1" aria-label="Digit 5">
  <input type="text" maxlength="1" aria-label="Digit 6">
</fieldset>

If pasting the full code into the first field only fills one digit, the pattern fails. The W3C document notes this explicitly: the failure applies unless pasting into the first input automatically populates the remaining fields.

Pattern 2 — Selective character entry:

<!-- FAILURE: User must mentally extract specific characters -->
<fieldset>
  <legend>Enter the 2nd, 6th, and last characters of your password</legend>
  <label>2nd character: <input type="password" maxlength="1"></label>
  <label>6th character: <input type="password" maxlength="1"></label>
  <label>Last character: <input type="password" maxlength="1"></label>
</fieldset>

Pattern 3 — Dropdown character selection:

<!-- FAILURE: Each character selected from a dropdown -->
<fieldset>
  <legend>Enter your 4-character PIN</legend>
  <select aria-label="Character 1"><option>A</option>!-- ... --></select>
  <select aria-label="Character 2"><option>A</option>!-- ... --></select>
  <select aria-label="Character 3"><option>A</option>!-- ... --></select>
  <select aria-label="Character 4"><option>A</option>!-- ... --></select>
</fieldset>

All three prevent what the standard calls entering a credential "in the same format" as it was created.

Why This Matters

For a screen reader user, a keyboard navigator, or someone using switch access, split-field authentication isn't just inconvenient — it transforms a routine login into a multi-step cognitive task. Password managers cannot fill split fields reliably. Clipboard paste is blocked or degraded. The user must either memorize the credential, transcribe it from another source character by character, or give up.

That last option — giving up — is the real-world outcome that accessibility standards exist to prevent. SC 3.3.8 and 3.3.9 exist because authentication is a gateway. Block the gateway, and every accessible feature behind it becomes irrelevant.

Users with cognitive disabilities — including those with memory impairments, attention difficulties, or processing differences — are disproportionately affected. But the impact extends further. Users with motor disabilities who rely on paste-based input, users with low vision who copy codes from a separate authenticator app, and users who simply cannot hold a six-digit sequence in working memory while tabbing between six fields all encounter the same wall.

The W3C document frames this precisely: preventing paste "results in a cognitive function test." That framing matters. SC 3.3.8 prohibits cognitive function tests as the sole authentication mechanism. Split fields that block paste are exactly that.

The Fix

The corrected pattern is architecturally simple:

<!-- CORRECT: Single input, paste enabled, autocomplete supported -->
<label for="totp-code">Enter your 6-digit verification code</label>
<input 
  type="text" 
  id="totp-code" 
  inputmode="numeric" 
  autocomplete="one-time-code" 
  maxlength="6"
  pattern="[0-9]{6}"
>

For TOTP codes specifically, autocomplete="one-time-code" enables browser and OS-level autofill from SMS or authenticator apps — a direct accessibility win that also improves usability for all users. For passwords, autocomplete="current-password" or autocomplete="new-password" signals to password managers that they can fill the field.

If a design team is committed to a split-field visual layout for aesthetic reasons, the minimum requirement is that pasting into the first field automatically distributes characters across subsequent fields via JavaScript. This is technically achievable, though it introduces its own fragility — and a single input remains the more robust solution.

The related success criteria apply to any authentication technology. F109 is not web-specific. Native mobile apps, kiosk interfaces, and enterprise portals all fall within scope.

Applying This in Practice

For teams auditing existing authentication flows, this failure has a specific detection profile. Automated tools will not reliably catch it — the gap between automated detection and manual review is well-documented, and interaction-dependent failures like F109 require functional testing.

A practical code review checklist for authentication forms:

The paste-blocking check is the most actionable: search your codebase for onpaste, e.preventDefault() inside paste handlers, and maxlength="1" on authentication inputs. Those three patterns together are a strong signal of F109.

Organizations managing multiple compliance frameworks simultaneously — WCAG 2.2, Section 508, EN 301 549 — should note that SC 3.3.8 is a WCAG 2.2 addition. If your team is still primarily working against a WCAG 2.1 baseline, this criterion may not yet be on your radar. The compliance framework landscape makes these gaps predictable. Authentication is a high-frequency, high-stakes interaction — it warrants explicit inclusion in any WCAG 2.2 gap analysis.

CORS Perspective

F109 is a useful case study in how a single technical decision — splitting a credential field — compounds across all four analytical dimensions. The community impact is concrete: users with cognitive and motor disabilities are blocked at the authentication gate, before they can access any service. Operationally, the fix is low-cost relative to its impact, which puts it squarely on the "chop list" of high-value quick wins — but only if teams are running functional testing rather than relying on automated scans alone. The risk profile is clear: SC 3.3.8 is a Level AA requirement, meaning it applies to most public-sector and federally-funded digital services under current Title II and Section 508 obligations. Strategically, authentication accessibility is a rare case where the fix — a single input with proper autocomplete — simultaneously improves security posture (password manager adoption reduces reuse), reduces support burden, and addresses a documented civil rights barrier. Leadership alignment arguments write themselves.