--- title: Build scanner-safe double opt-in | daily.dev description: Email security scanners can inadvertently confirm subscriptions by following GET links before the recipient does. The solution is a two-step double opt-in: a... canonical: https://daily.dev/posts/build-scanner-safe-double-opt-in-qgdlkj42f twitter:card: summary_large_image twitter:site: @dailydotdev og:type: website og:site_name: daily.dev og:title: Build scanner-safe double opt-in | daily.dev og:description: Email security scanners can inadvertently confirm subscriptions by following GET links before the recipient does. The solution is a two-step double opt-in: a... og:url: https://daily.dev/posts/build-scanner-safe-double-opt-in-qgdlkj42f og:image: https://api.daily.dev/og/posts/qgdLkJ42F.png og:image:alt: Build scanner-safe double opt-in og:image:width: 1200 og:image:height: 630 og:locale: en --- > ## Documentation Index > Fetch the complete documentation index at: https://daily.dev/llms.txt > Use this file to discover all available pages before exploring further. # Build scanner-safe double opt-in **[Flavio Copes](https://daily.dev/sources/flaviocopes)** · 4 min read · 0 upvotes · 0 comments ## Summary Email security scanners can inadvertently confirm subscriptions by following GET links before the recipient does. The solution is a two-step double opt-in: a GET request renders a confirmation page with a hidden form, while a POST request performs the actual confirmation. Key implementation details include generating a 32-byte random token sent via email, storing only an HMAC hash in the database, using an atomic SQL UPDATE that nullifies the token on success (making it single-use), setting response headers to prevent token leakage (no-store, no-referrer, noindex), keeping the token in the POST body rather than the URL, and expiring pending confirmations after 24 hours via a scheduled cleanup query. CSRF protection is unnecessary since the 256-bit token itself serves as the authorization boundary. ## Full article daily.dev links to this article rather than hosting it. Read it at the original source: ## Similar posts on daily.dev - [Your sign-up form is a weapon](https://daily.dev/posts/your-sign-up-form-is-a-weapon-cwnsa8fnc) · Hacker News · 0 upvotes · 0 comments - [Build idempotent double opt-in signup](https://daily.dev/posts/build-idempotent-double-opt-in-signup-pqalhwsrt) · Flavio Copes · 1 upvotes · 0 comments - [How I Found and Bypassed a Newsletter Confirmation System \(IDOR\).](https://daily.dev/posts/how-i-found-and-bypassed-a-newsletter-confirmation-system-idor--0mtxfpcsl) · InfoSec Write-ups · 0 upvotes · 0 comments - [GHSA-57hq-95w6-v4fc \(devise\): Confirmable "change email" race condition permits user to confirm email they have no access to](https://daily.dev/posts/ghsa-57hq-95w6-v4fc-devise-confirmable-change-email-race-condition-permits-user-to-confirm-emai-xuuvn4m4d) · RUBYLAND · 0 upvotes · 0 comments - [Status pages can now email your subscribers](https://daily.dev/posts/status-pages-can-now-email-your-subscribers-vpbu62m0l) · Oh Dear · 0 upvotes · 0 comments --- Tags: [#security](https://daily.dev/tags/security), [#authentication](https://daily.dev/tags/authentication), [#cloudflare](https://daily.dev/tags/cloudflare) [View this post on daily.dev](https://daily.dev/posts/build-scanner-safe-double-opt-in-qgdlkj42f) ```json {"@context":"https://schema.org","@graph":[{"@type":"Organization","@id":"https://daily.dev/#organization","name":"daily.dev","url":"https://daily.dev","logo":{"@type":"ImageObject","url":"https://daily.dev/apple-touch-icon.png","width":180,"height":180},"sameAs":["https://twitter.com/dailydotdev","https://github.com/dailydotdev","https://www.linkedin.com/company/daily-dev-ltd"]},{"@type":"WebSite","@id":"https://daily.dev/#website","url":"https://daily.dev","name":"daily.dev","publisher":{"@id":"https://daily.dev/#organization"},"potentialAction":{"@type":"SearchAction","target":{"@type":"EntryPoint","urlTemplate":"https://daily.dev/search?q={search_term_string}"},"query-input":"required name=search_term_string"}}]} {"@context":"https://schema.org","@type":"TechArticle","headline":"Build scanner-safe double opt-in","url":"https://daily.dev/posts/build-scanner-safe-double-opt-in-qgdlkj42f","mainEntityOfPage":{"@type":"WebPage","@id":"https://daily.dev/posts/build-scanner-safe-double-opt-in-qgdlkj42f"},"datePublished":"2026-08-05T14:25:18.930Z","dateModified":"2026-08-05T14:25:43.632Z","description":"Email security scanners can inadvertently confirm subscriptions by following GET links before the recipient does. 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