WHATSAPP-002 — Link a verified WhatsApp number and versioned consent to a member UID

[daliu]

Outcome

If WHATSAPP-001 selects one-to-one Cloud API use, let a signed-in member prove control of a WhatsApp number and record narrowly scoped consent.

Scope

• Generate a one-time server code sent through an approved authentication template.
• Hash the code; make it short-lived, one-use, rate/attempt limited, and App Check protected.
• Normalize phone/WhatsApp identifiers server-side and prevent silent multi-UID ownership.
• Record versioned consent separately for access/admin notices and optional announcements/marketing.
• Provide opt-out, reassignment/recovery, deletion, and audited conflict handling.

Acceptance criteria

• WhatsApp proof links only a channel; it never authenticates Firebase or grants membership/discounts.
• Wrong, expired, replayed, enumerated, duplicate-phone, abuse, opt-out, and recovery paths are tested in sandbox/emulators.
• Codes, phone values, tokens, and provider bodies never appear in logs/errors/issues.
• No production message is sent by local or CI tests.
• Template/category use and consent comply with the owner-approved policy.

Dependencies

#85 must select Cloud API; #81; coordinating backlog AUTH-001 and ABUSE-001.

Official references

• https://developers.facebook.com/documentation/business-messaging/whatsapp/getting-opt-in
• https://developers.facebook.com/documentation/business-messaging/whatsapp/templates/authentication-templates/authentication-templates
• https://developers.facebook.com/documentation/business-messaging/whatsapp/webhooks/create-webhook-endpoint

Coordination

Parent: #79

Do not begin implementation until dependencies are complete, this issue is assigned, and a timestamped CLAIMED comment naming the agent and branch is posted. Creation of this ticket is not a claim. Preserve the parallel agent work tracked by stable IDs in GITHUB_ISSUES.md.