Zsign

Documentation from azlabsio/zsign-plugin, recorded October 23, 2026. APIs and setup may differ in the Bijection adaptation.

@zsign/convex

zSign e-signature component for Convex. An app installs this component to send a document for signature, observe envelope progress reactively, run completion callbacks, and retrieve the signed PDF + completion certificate when done.

Published on npm as @zsign/convex. example/ is the minimal authenticated demo app it was proven with. Agent-facing install/use guide: SKILL.md.

Install

Copy codenpm install @zsign/convex

Copy code// convex/convex.config.ts
import { defineApp } from "convex/server";
import zsign from "@zsign/convex/convex.config.js";

const app = defineApp();
app.use(zsign, {
  env: {
    ZSIGN_API_KEY: process.env.ZSIGN_API_KEY,
    ZSIGN_API_BASE_URL: process.env.ZSIGN_API_BASE_URL,
    ZSIGN_WEBHOOK_SECRET: process.env.ZSIGN_WEBHOOK_SECRET,
    ZSIGN_WEBHOOK_SECRET_PREVIOUS: process.env.ZSIGN_WEBHOOK_SECRET_PREVIOUS,
  },
});
export default app;

Env (component, declared in convex.config.ts)

• ZSIGN_API_KEY (required) — zs_live_…/zs_test_… org key.
• ZSIGN_API_BASE_URL (optional) — defaults to https://zsign.io. An origin; a trailing /api or /api/v1 (as the zSign API docs write it) is stripped.
• ZSIGN_WEBHOOK_SECRET (optional) — whsec_…; required to verify webhook signatures.
• ZSIGN_WEBHOOK_SECRET_PREVIOUS (optional) — previous whsec_…, accepted in parallel during secret rotation.

App usage

Copy codeimport { Zsign } from "@zsign/convex";
import { components } from "./_generated/api";

const zsign = new Zsign(components.zsign);

// Action: send. operationId is your idempotency/correlation key — replays
// return the stored result instead of creating a second envelope.
await zsign.send(ctx, {
  file, filename: "proposal.pdf",
  recipients: [{ name, email, role: "client", signingOrder: 1 }],
  operationId, // required; also sent as the HTTP Idempotency-Key
  metadata: { dealId: "..." }, // strings only; zsign.* keys are reserved
});
// -> { documentId, sessionId, signingUrls, replayed? }

// Queries: reactive reads (subscribe from UI or use in other functions)
await zsign.status(ctx, operationId); // envelope + recipients + completion ids
await zsign.list(ctx, { activeOnly: true }); // non-terminal envelopes

// Actions: canonical sync + artifacts
await zsign.refresh(ctx, operationId); // force a GET against the zSign API
await zsign.getSignedPdf(ctx, completedDocumentId); // -> ArrayBuffer
await zsign.getCertificate(ctx, documentId);        // -> ArrayBuffer

Webhooks

Component http routes did not mount on the self-hosted backend this was built against, so the app wires one route itself using the shipped verifier:

Copy code// convex/http.ts
import { httpRouter } from "convex/server";
import { verifyWebhookRequest } from "@zsign/convex";
import { internal } from "./_generated/api";

const http = httpRouter();
http.route({
  path: "/zsign/webhook",
  method: "POST",
  handler: httpAction(async (ctx, request) => {
    const res = await verifyWebhookRequest(request, [
      process.env.ZSIGN_WEBHOOK_SECRET,
      process.env.ZSIGN_WEBHOOK_SECRET_PREVIOUS,
    ]);
    if (!res.ok) return new Response(res.error, { status: res.status });
    try {
      await ctx.runMutation(components.zsign.lib.applyWebhookEvent, res.event);
    } catch {
      return new Response("webhook receipt unavailable", { status: 503 });
    }
    return new Response("ok", { status: 200 });
  }),
});
export default http;

Verified signature (X-Webhook-Signature: t=…,v1=…, HMAC-SHA256 over t.{raw_body}, 300s tolerance, either current or previous secret) happens before any mutation; unknown X-Webhook-Ids are deduped; unknown sessions are persisted as orphaned events and replayed onto the envelope if it appears later. A receipt failure returns 503 so zSign retries delivery.

Completion callbacks

Copy code// internal mutation the app owns
export const onEnvelopeCompleted = internalMutation({
  args: {
    callbackId: v.string(), operationId: v.string(), sessionId: v.string(),
    documentId: v.string(), completedDocumentId: v.string(),
    metadata: v.record(v.string(), v.string()),
  },
  handler: async (ctx, args) => { /* advance your workflow */ },
});

// drain (e.g. from a cron action)
await zsign.onCompleted(ctx, internal.myFunctions.onEnvelopeCompleted);

Handlers are mutations. Each (envelope, kind) callback is deduped and persisted; a handler that throws stays failed with lastError and is retried by the next drain — at-least-once, not exactly-once.

Reconciliation

Webhook-driven state is guarded by generation + status rank; on a conflict (out-of-order or inconsistent event) the component schedules reconcile.refreshEnvelope, which fetches GET /api/v1/documents/{id} and applies canonical state only if the generation still matches, with bounded backoff. terminal envelopes are never refreshed. lastSyncedAt / syncError surface per-envelope health; zsign.refresh(ctx, operationId) forces a manual sync.

Verified end-to-end (2026-09-14)

Stack: self-hosted ghcr.io/get-convex/convex-backend (docker, :3210/:3211), local zSign backend (:7101, local Postgres + local_gcs_uvicorn.py), webhook http://127.0.0.1:3211/zsign/webhook.

1. Send — component action builds multipart manually (Convex runtime's FormData drops Blob MIME; zSign 422s without application/pdf), POSTs with Idempotency-Key = operationId. Tags {signature*:client} auto-assign to role: "client".
2. Webhooks → reactive status — all lifecycle events delivered, 200 each; status completed with completedDocumentId (the completed doc's id — document.completed's data.document_id is NOT the original).
3. Callbacks — document.completed persisted an onCompleted callback; a failing drain recorded lastError, and the next drain retried it to succeeded. The example app's completions row was written by its own internalMutation handler.
4. Artifacts — signed PDF (tags redacted, signature stamped) and certificate both return bytes through component actions.
5. Signature verification — good sig → applied; replayed X-Webhook-Id → "duplicate"; bad sig / stale t → 401; ZSIGN_WEBHOOK_SECRET_PREVIOUS accepted.
6. Replay — send twice with the same operationId → {replayed: true, same documentId}; with PR #393's Idempotency-Key the upstream call also collapses to one envelope + one debit.
7. Auth wrappers (example) — token-authenticated sendEnvelope / envelopeStatus / listEnvelopes / refreshEnvelope / artifact fetches; bad token → unauthenticated, wrong tenant → not found.
8. Packed artifact — npm pack → installed into a clean app dir → convex codegen + tsc clean, Zsign client types resolve.

Failure semantics

• Webhook receipt: verify → dedupe → persist. Unknown envelope → orphaned row, re-attached on insertEnvelope by sessionId.
• Send: operation allocated before the HTTP call; a network/5xx failure marks it failed and a retry re-sends; a sent op short-circuits to the stored result.
• Reconcile: generation guard drops stale applies; bounded backoff then stops.
• Callbacks: deduped, persisted, failure-visible, retryable — at-least-once.

zSign has no staging environment, so external-email checks used a dedicated, clearly labeled live account (signup → 0 credits, email verify grants 3, one send debits exactly 1, invitation delivered).

Agent plugin pack

This repo also ships the zSign agent plugin pack at the root — the same files Cursor uses to connect to the remote MCP server. They are not part of the npm package (files limits the tarball to src/, docs/, SKILL.md, CHANGELOG.md).

• plugin.json — Agent Plugins 1.0.0 manifest
• mcp.json — remote Streamable HTTP MCP server at https://zsign.io/mcp (OAuth 2.1 with Dynamic Client Registration; no API key header once OAuth completes, no secret stored in the pack)
• .cursor-plugin/plugin.json — Cursor logo and homepage (Agent Plugins plugin.json has no logo field)
• assets/logo.svg — copied from frontend/public/favicon.svg

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