AuthResend Audience Contact Sync

Resend Audience Contact Sync

When a user signs up or is deleted, Better Auth databaseHooks trigger ResendContactService to add or remove a contact from the configured Resend audience....

Resend Audience Contact Sync

User lifecycle → Resend audience — how Bloqr keeps the Resend "Bloqr Users" audience in sync with the D1/Neon user database.

Overview

When a user signs up or is deleted, Better Auth databaseHooks trigger ResendContactService to add or remove a contact from the configured Resend audience. This happens fire-and-forget via ctx.waitUntil() — the user-facing response is never delayed by audience sync.

Architecture

Services

ResendApiService (worker/services/resend-api-service.ts)

Typed REST wrapper for the Resend Contacts/Audiences API. This is the only place in the codebase that calls https://api.resend.com/audiences/* — all other code uses this service.

  • Zod-validates all request payloads before sending
  • Validates all API responses against typed Zod schemas
  • Throws ResendApiError (typed, carries statusCode + errorName) on non-2xx responses
  • Uses fetch() directly — no Resend SDK dependency

ResendContactService (worker/services/resend-contact-service.ts)

Business logic layer for user lifecycle sync.

  • syncUserCreated(user) — calls ResendApiService.createContact()
  • syncUserDeleted(user) — calls ResendApiService.deleteContact()
  • All errors are caught and logged as warnings — never rethrown
  • Name splitting: "Alice Smith" → firstName: "Alice", lastName: "Smith"

NullResendContactService

No-op implementation returned by createResendContactService() when either RESEND_API_KEY or RESEND_AUDIENCE_ID is absent. Implements IResendContactService so call sites are unconditional — no if (contactSvc) guards needed.

Configuration

Production secrets

# Set the Resend API key (shared with email send path)
wrangler secret put RESEND_API_KEY
# Value: re_xxxxxxxxxxxx (from https://resend.com/api-keys)

# Set the audience ID
wrangler secret put RESEND_AUDIENCE_ID
# Value: xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx
# (from https://resend.com/audiences → create "Bloqr Users" → copy UUID)

Local development

Add to .dev.vars:

RESEND_API_KEY=re_test_xxxxxxxxxxxx
RESEND_AUDIENCE_ID=xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx

Resend dashboard setup

  1. Go to resend.com/audiences
  2. Create an audience named "Bloqr Users"
  3. Copy the audience UUID — this becomes RESEND_AUDIENCE_ID
  4. Ensure bloqr.dev is a verified domain in resend.com/domains

Sequence Diagrams

User sign-up

User deletion

Error Handling

All sync errors are caught inside ResendContactService and logged at console.warn level. They never propagate to the auth response:

[ResendContactService] syncUserCreated failed: ResendApiError 422 (validation_error): Contact already exists
[ResendContactService] syncUserDeleted failed: ResendApiError 404 (not_found): Contact not found

A ResendApiError 422 on syncUserCreated is normal for re-registrations (same email, new account). It is non-fatal.

A ResendApiError 404 on syncUserDeleted means the contact was already removed or never synced. It is non-fatal.

Testing

# Unit tests (no HTTP calls — uses stub ResendApiService)
deno test worker/services/resend-contact-service.test.ts

# API service tests (patches globalThis.fetch)
deno test worker/services/resend-api-service.test.ts

See Also

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