ADR-013: Phone codes by SMS through Textbridge

Status: accepted · Date: 6 May 2026 · Decided by: Piet de Vries, Elif Yildiz, Rafael Duarte, Lena Fischer

Context

Lena's initiative "Phone codes for depot workers without email" (ENG-1418) lets people without a company email sign in with a code. Greenhollow Dairy and Northgate want it first. These people have a phone, mostly not a smartphone they want to install anything on, and no email for a password reset.

Options:

1. Codes by SMS through a provider.
2. An authenticator app. Most depot workers won't install one on a personal phone.
3. Codes printed by an administrator. Doesn't scale, and codes end up on noticeboards.

Providers looked at: Textbridge and two others. Textbridge covers the UK, Ireland and the EU countries we need, returns delivery receipts by webhook, and costs about €0.04 a message in our volumes.

Decision

• Six-digit codes, valid ten minutes, five tries, then a 15-minute wait.
• identity-service asks notifier for the SMS directly, not through the outbox, so the code leaves within a second (ADR-004 expected this).
• One provider, Textbridge, for every region.

Consequences

• If Textbridge is down for a country, phone-code sign-in stops there. No fallback.
• We need delivery-receipt monitoring, not only "we sent it".
• Phone numbers are personal data at a third party; Textbridge goes on the sub-processor list.

Updates

• 9 September 2026 (Elif): after OPS-33 we started "Text codes through a second SMS provider". It is postponed until Textbridge's EU contract is settled. One provider for now; the receipt-lag alarm and the status page are what we have.