security: implement signing approval popup (replace silent auto-approve)

[jjohare]

Summary

• Replace showPermissionPrompt() auto-approve stub with a real popup-based approval flow
• New popup/approve.html + popup/approve.js: Approval dialog showing origin, action, and event preview
• 60-second auto-deny timeout prevents abandoned prompts from blocking indefinitely

Security Impact (CRITICAL)

This is the most critical security fix. The current showPermissionPrompt() implementation:

async function showPermissionPrompt(origin, action) {
  console.log(`[Podkey] Auto-approving: ${origin} wants to ${action}`);
  return true; // <-- EVERY request is silently approved
}

Every website can silently sign Nostr events as the user. A malicious page can:

1. Call window.nostr.signEvent() to sign arbitrary events (posts, DMs, delegation tokens)
2. Call window.nostr.getPublicKey() to identify the user
3. The user sees no prompt, no notification, nothing

This completely defeats the purpose of a signing extension. The user's identity is effectively compromised the moment they visit any page with JavaScript.

How the Fix Works

The new flow follows the established pattern used by nos2x, Alby, and other NIP-07 extensions:

1. Website calls window.nostr.signEvent(event)
2. Content script forwards to background service worker
3. showPermissionPrompt() generates a unique requestId and opens popup/approve.html via chrome.windows.create()
4. The popup displays:
   • The requesting origin (e.g., https://evil-site.com)
   • The action being requested (e.g., "sign an event (kind 1)")
   • A preview of the event data (kind, truncated content, tag count)
   • A countdown bar showing the 60-second timeout
5. User clicks Approve or Deny
6. approve.js sends APPROVE_SIGNING message back to background
7. Background resolves the pending Promise and proceeds accordingly

If the user closes the popup without clicking, the beforeunload handler sends a deny. If 60 seconds pass with no response, the request is auto-denied.

Files Changed

File	Change
src/background.js	Replace auto-approve with popup-based showPermissionPrompt(); add pendingApprovals Map; handle APPROVE_SIGNING messages; pass event preview data to prompts
popup/approve.html	New approval dialog with origin badge, action text, event preview, approve/deny buttons, timeout countdown bar
popup/approve.js	Handle URL params, wire up approve/deny buttons, send APPROVE_SIGNING messages, deny on window close

Test plan

• Load extension, visit a test page that calls window.nostr.getPublicKey() -- verify approval popup appears
• Click Deny -- verify the calling page receives an error
• Click Approve -- verify the calling page receives the public key
• Test window.nostr.signEvent() -- verify popup shows event kind and content preview
• Close the popup window without clicking a button -- verify request is denied
• Wait 60 seconds without interacting -- verify request is auto-denied
• Verify trusted origins still auto-approve for Solid auth events (kind 27235) with auto-sign enabled
• Verify the popup opens focused and in front of the browser window

[Copilot]

Pull request overview

This PR addresses a critical security gap in the signing flow by replacing the background service worker’s silent auto-approval with an explicit user approval popup before releasing a public key or signing events.

Changes:

• Implement a real showPermissionPrompt() that opens an approval popup and resolves via a pendingApprovals map in the background worker.
• Add a new approval UI (popup/approve.html + popup/approve.js) that shows origin/action plus a small event preview.
• Add a 60-second auto-deny timeout in the background to prevent hanging requests.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 4 comments.

File	Description
src/background.js	Replaces auto-approve stub with popup-based approval flow and request tracking/timeout.
popup/approve.html	Adds a dedicated approval dialog UI for signing/permission requests.
popup/approve.js	Wires the approval UI to send approve/deny messages back to the background worker.

Comments suppressed due to low confidence (1)

src/background.js:325

• formatEventForPrompt() is now unused after switching the signing prompt to pass previewData JSON into showPermissionPrompt(). Please remove this dead code (or re-use it to build the popup preview) to avoid confusing future maintenance.

/**
 * Format event for display in prompt
 */
function formatEventForPrompt (event) {
  const lines = [];

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[jjohare]

Folded into #22 — a single CI-green, adversarially-reviewed PR that consolidates this branch with the other security fixes plus NIP-44 and residual gap-fixes (exact-host trust, NIP-98 nonce, signEvent self-verify, honest provider surface, auto-sign default OFF). Suggest reviewing/merging #22; this can be closed in its favour.

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[jjohare]

Superseded by #22 (merged as 384918d), which consolidates this branch's fixes into one reviewed, CI-green change. Closing in favour of that.