SERVICES / PLAID & FINTECH INTEGRATION
A Plaid integration that survives production, not just the sandbox.
Transactions, investment holdings, liabilities, and webhooks: idempotent, signature-verified, and encrypted at the column level, built by an engineer who operates one of these in production.
01
WHO THIS IS FOR
- Fintech and personal-finance products integrating Plaid (or a comparable aggregator) for the first time.
- Teams with an existing Plaid integration that's accumulated correctness or security debt: duplicate transactions, unverified webhooks, access tokens sitting in plaintext columns.
- Products expanding from transactions-only into investments and liabilities, where the data model and sync logic get materially more complex.
02
WHAT'S INCLUDED
- Webhook handling with cryptographic signature verification: Plaid's ES256 JWT signature validated against their published JWKs, the
request_body_sha256claim checked against the actual raw request body (not the parsed JSON, which can re-serialize differently), and a tight max-age window that rejects replayed webhooks. - Idempotency enforced at the database layer, not just in application logic — a unique constraint on the webhook's request identifier, insert-first with unique-violation treated as "already processed." This survives retries, redeploys, and duplicate delivery, which application-level de-duplication alone does not.
- Sync architecture for transactions, investment holdings, and liabilities, including reconciliation jobs that catch drift between what Plaid reports and what's stored.
- Column-level encryption for access tokens, item IDs, and account identifiers: AES-256-GCM with a per-tenant data key, so a database dump alone doesn't leak usable credentials. Where an encrypted column needs a unique-index lookup (e.g., "have we seen this Plaid item before?"), a deterministic blind-index hash stands in for ever comparing plaintext.
- CSV import paths for data sources that don't have an API (e.g., brokerage position exports), normalized into the same data model as the API-sourced data.
- Cost and call-volume awareness. Plaid billing is metered per product and per institution; sync design accounts for that from the start, not after the first invoice surprise.
03
ENGAGEMENT SHAPES
- Assessment (1 week, fixed fee): review of an existing integration against the failure modes above — webhook idempotency, signature verification, token storage, retry/backoff behavior. Delivered as a prioritized findings doc.
- Sprint (2–5 weeks, fixed scope): build or rebuild a defined slice — e.g., "add investments sync" or "replace unverified webhook handling with signature-verified, idempotent processing."
- Retainer: ongoing ownership of the Plaid integration as the product and Plaid's own API surface evolve.
04
FAQ
Q1We already have a Plaid integration — is a rebuild really necessary?
Usually not a full rebuild. Most integrations that "mostly work" have a specific set of gaps (webhook verification, idempotency, token encryption) that can be closed incrementally. The assessment exists specifically to tell you which gaps you actually have before committing to a bigger scope.
Q2Do you work with aggregators other than Plaid?
Plaid is the deepest experience, but the underlying patterns (webhook idempotency, token encryption, retry-safe sync) apply to any account-aggregation API. Say which one you're on in the intro call.
Q3How do you handle Plaid's sandbox-vs-production behavior differences?
By building against realistic failure modes from the start — duplicate webhooks, delayed initial syncs, institution-level errors — rather than only the happy path the sandbox tends to produce.
GET IN TOUCH