OTP (One-Time Password)

A one-time password (OTP) is a temporary, automatically generated code sent to a user via email or SMS that is valid for a single authentication session. Unlike static passwords, an OTP expires after a short window — typically a few minutes — and cannot be reused. In digital publishing, OTPs serve as a verification mechanism to confirm that a reader actually owns the email address they provided before granting access to [gated content](/glossary/gated-content). This prevents fake submissions and ensures that every captured contact is a real, reachable person.

Without email verification, lead capture forms are vulnerable to junk submissions. Readers may enter misspelled addresses, disposable emails, or entirely fabricated contacts, degrading the quality of your lead database over time. OTP verification solves this by requiring proof of email ownership before content access is granted. The result is a cleaner, more reliable contact list where every address has been confirmed as valid and deliverable. For publishers distributing confidential or premium content, OTPs also act as an access control layer, ensuring that only verified recipients can view sensitive material and that forwarded links cannot be used without re-verification.

FlipLink supports OTP verification as part of its [lead capture](/features/lead-capture) and [privacy and access control](/features/privacy-and-access-control) features. When a publisher enables OTP on a lead capture form, the reader enters their email address and receives a six-digit verification code at that address. The reader then enters the code to confirm their identity, and only after successful verification is the publication content unlocked. This works alongside [email allowlisting](/glossary/email-allowlist) for layered access control — you can restrict which email domains are allowed and then verify each individual address with OTP. The entire process takes seconds for the reader while dramatically improving the quality of captured lead data.

**Expiration window.** OTP codes should expire quickly — FlipLink's codes are time-limited to prevent delayed reuse. If a code expires, the reader simply requests a new one. **Single-use enforcement.** Each code is invalidated after a single successful entry. Even if someone intercepts a code after it has been used, it provides no access. **Rate limiting.** OTP systems need protection against brute-force attempts. Sending too many verification requests from the same session or IP should trigger throttling to prevent abuse. **Channel security.** Email-based OTPs are only as secure as the recipient's email account. For highly sensitive content, combine OTP with [password protection](/glossary/password-protection) for two independent verification layers.

OTP systems typically use one of two approaches: time-based (TOTP) where the code is derived from the current timestamp, or event-based (HOTP) where the code is generated per request. In the context of digital publishing, event-based codes are more common since the verification happens once at the point of content access rather than on a recurring schedule. The verification flow follows a standard pattern: 1. Reader submits their email address in the lead capture form 2. Server generates a random code and stores a hashed version with an expiration timestamp 3. Code is delivered to the reader's email inbox 4. Reader enters the code in the verification prompt 5. Server compares the submitted code against the stored hash 6. On match, access is granted and the code is invalidated FlipLink processes the entire flow server-side, so no sensitive data is exposed in the browser. The verification state is tied to the reader's session, and the code cannot be reused across different sessions or publications.

**What happens if the reader does not receive the OTP?** The reader can request a new code. Common causes include spam filters catching the verification email or slow mail server delivery. Checking the spam/junk folder usually resolves it. **Does OTP verification slow down the reader experience?** The additional step takes roughly 15-30 seconds. Most readers are familiar with OTP flows from banking and e-commerce, so the friction is minimal. The trade-off is a substantially higher quality lead list. **Can OTP be combined with other access controls?** Yes. In FlipLink, OTP can work alongside [email allowlisting](/glossary/email-allowlist) and [password protection](/glossary/password-protection). For example, you can restrict access to company email domains, verify each address with OTP, and still require a shared password — three independent layers.