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How account activation works
Registration and activation are separate steps. A user submits an email address and registration details; your application stores a pending account and sends a verification link to that address. The link demonstrates control of the submitted mailbox. Only successful verification should change the associated account to active and permit ordinary use.
This distinction matters: a user who has not verified an address must not gain access to protected application functions just because registration succeeded. OWASP recommends verifying email ownership before enabling account use. See the OWASP Email Validation and Verification Cheat Sheet.
Configure Vaadin and Spring Security
Vaadin Flow applications use Spring Security for authentication. Vaadin’s login guide recommends configuring VaadinSecurityConfigurer.vaadin() and the intended login view. Simply adding Spring Security without a configured authentication mechanism can lock you out of the application during development.
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Plan access rules so registration and activation are reachable anonymously, while authenticated application views and account-management operations remain protected. Vaadin documents view access controls including @AnonymousAllowed, @PermitAll, @RolesAllowed, and @DenyAll, as well as Spring URL-pattern checks in its security guide. Choose a coherent access-control approach for each view; Vaadin cautions that mixing URL-pattern and view-based security for the same views can make the effective policy confusing. Confirm exact configuration against the Vaadin and Spring versions used by your project, since the linked documentation is rolling documentation.
Making a route public only permits anonymous navigation to that route; it must not make the pending account or protected services generally usable. Enforce authorization in application services as well as in the UI.
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Create a pending account and issue its activation token
1. Define email handling and account state
Validate the submitted address and set a documented policy for preserving, comparing, and normalizing it. Store the original address for communication. Email local-part and domain case handling differ, so do not indiscriminately lowercase the entire address unless your application’s policy and ownership of that behavior justify it. Keep the account pending until verification succeeds.
2. Generate and store a secure token
Generate an unpredictable token using a cryptographically secure random generator. Do not derive it from the email address, account ID, timestamp, or another guessable value. Associate it with the pending account, an expiration time, and a state that allows it to be consumed only once.
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Where feasible, persist a digest of the token rather than the raw value, and compare and consume it safely. This is a practical storage recommendation; the essential security properties are that the token is unguessable, time-limited, and single-use. Make token consumption safe under concurrent requests so two requests cannot both redeem the same token.
3. Build and email an absolute link
Construct the activation URL from a configured public application origin, not from an arbitrary incoming Host header. Send it to the submitted address and treat the URL as a bearer secret: anyone who obtains it may be able to activate the associated account. Do not log the complete token or expose it unnecessarily through analytics, proxy logs, or referrer data. Avoid third-party resources on the activation page where they could receive the token-bearing URL.
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Expose a public activation route and redeem the link
The activation view or endpoint must allow unauthenticated access, but the rest of the application should retain its intended restrictions. When the route receives a token, locate its record and validate that it exists, is unexpired, has not been consumed, and is associated with an account still awaiting verification.
Consume the token and activate only its associated pending account as one atomic operation. If the token is invalid, expired, or already used, fail safely without changing account state. An already-used link can lead to a neutral completion message or a controlled resend path; it should not reapply the activation operation. Avoid messages that reveal whether an arbitrary email address has an account.
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Control abuse and provide recovery
- Rate-limit registration, resend, and activation attempts.
- Use outwardly equivalent responses for existing and nonexistent email addresses, and avoid meaningful timing differences that could enable account enumeration.
- Set an expiration period and resend policy appropriate to your product’s threat model. There is no universal lifetime or resend schedule established by the cited guidance.
- Handle mail delivery failures without silently activating the account. Provide a safe way to request another link, subject to rate limits.
- Use a reliable transactional email sender and a canonical public base URL; no particular mail provider is required by Vaadin.
Should you use Spring Security One-Time Token Login?
Spring Security’s One-Time Token Login feature provides patterns for generating, delivering, and customizing one-time tokens, including a custom generation-success handler for delivery and a customizable OneTimeTokenService for expiry and persistence. Its documented purpose is passwordless sign-in, not proving ownership of an address during registration.
Use an application-owned verification workflow when registration must confirm mailbox ownership before enabling a new account. Consider One-Time Token Login when the product needs passwordless authentication. They are not interchangeable: a sign-in token should not automatically activate an account, and the current Spring reference notes that the OTT authentication provider does not validate disabled, locked, or expired account status by default. Bind successful registration verification explicitly to the pending account and its current verification state.
| Approach | Useful when | Decisions to make |
|---|---|---|
| Application-owned verification token and account-state workflow | Registration must prove email ownership before a new account is enabled. | Token storage and revocation, expiry, resend behavior, atomic single-use consumption, and auditability. |
| Spring Security One-Time Token Login | The product wants passwordless sign-in through a one-time token. | Sign-in semantics, token-service persistence and expiry, account-status validation, and delivery integration. |
Test the complete lifecycle
Before release, test the workflow with the Vaadin and Spring versions actually deployed. Include successful first use, unknown and expired tokens, replay, concurrent redemption, pending-account authorization denial, active-account access, resend limits, mail delivery failure, and anonymous access to the activation route. These checks help verify both the state transition and the boundary between public verification and protected application features.
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