Sign in with lemma.id | Passwordless login with no user data to store

Built for any site that just needs login. Apps, tools, communities, marketplaces, anywhere you want returning users without collecting emails, phone numbers, or passwords first.

What sign-in looks like

A visitor clicks Sign in with lemma.id and approves a passkey. Your backend gets a signed proof carrying a stable ID that only your site ever sees. That ID is their account key: no signup form, no verification email, no password reset flow, ever. The same person gets the same ID on every return visit.

Why developers pick it

What other sign-in systems can't give you

It's not just passwordless. It changes what your servers have to hold and who sits in your login path.

Nothing to breach

Your user table is one opaque ID per account. No emails, no phone numbers, no password hashes. A database leak exposes identifiers that mean nothing anywhere else.

Private by structure

Every site gets a different ID for the same person, so users can't be correlated across sites. lemma.id can't profile your users or sell ads against them, because it never learns who they are.

Not in your login path

Your backend verifies proofs locally with an open verifier library. No API key to provision, no per-login call to lemma.id, and your account records stay yours.

One integration, room to grow

Start with free sign-in. Step up when a ban has to stick.

Login is free and covers most sites. When new-account rotation becomes the attack, require a human proof on the same integration, and the same account ID, without migrating anyone.

Passkey sign-in · free

Passwordless login with a stable, site-private account ID. The same person returns as the same ID every time. This is the default, and it's all most sites need. It doesn't stop someone from making another account, since anyone can create another lemma.id.

Presence proof

A fresh passkey at presentation signing shows the holder is at the device right now. Use it on sensitive actions like payouts or deletions, without adding OTP codes.

Human proof

One account per verified human, same account ID. When you ban someone, coming back means passing identity verification again. Add it per action when abuse shows up; nothing about your login changes.

For your users

One lemma.id works everywhere. No account per site.

Users create a lemma.id once, secured by their device passkeys, and sign in to every lemma.id-enabled site with it. Each site sees a different ID, so there's no profile following them across the web, and no company that can sell ads against their logins.

Why teams choose lemma.id

Compare it to the sign-in you'd build instead

Every login option makes you custodian of something: passwords, emails, or a big provider's shared user ID. Sign in with lemma.id is the option where there's nothing to hold.

	Sign in with lemma.id	Google / social SSO	Email + password
Your servers store	One site-private ID per user	Email, name, shared `sub`	Emails, password hashes, reset tokens
Who sees your users' logins	No one. Verification runs on your servers	The identity provider, on every login	Only you, but you hold the secrets
Cross-site tracking	Different ID per site, nothing to correlate	Same identity across every app	Email reused everywhere
Signup friction	One passkey approval, no form	OAuth redirect + consent screen	Form, verification email, password rules
Ban survives rotation requires human proofs	Step up to one account per verified human	Attacker rotates email or OAuth account	Attacker rotates emails

Full trust & data comparison →

How it works

Drop in, approve, verify

One script tag on the front end, one verifier library on your backend. lemma.id is not in the request path after that.

1

Drop in the button

Add the <lemma-signin> element with your hostname as the site ID. No registration, no API key, no dashboard step.

2

User approves a passkey

First-time visitors get a lemma.id in the popup; returning users just confirm. Either way your page receives a signed presentation.

3

Verify on your backend

The open verifier library checks the proof locally and hands you a stable, site-private ID. Use it as your account key and issue your own session.

Your login stack today

Signup form → verification email → password database → reset flows → OTP codes for anything risky → a breach target you maintain forever

With Sign in with lemma.id

Passkey approval → site-private account ID → local verification → step up to presence or human proofs where it matters → nothing sensitive to store

Verification flow, recovery, and data model →

Verifiable audit stamps

Prove a verified human did it, later

Stamp a checkout, post, or moderation call with an offline-verifiable proof. Evidence stays in your systems, re-check years later without calling lemma.id.

Stamp at the action

The SDK's stamp() helper attaches a signed credential to any event your backend records.

Verify offline

Same local verifier you use at signup. No network call on audit review day.

Your data, your systems

lemma.id doesn't store your logs. Useful for chargebacks, regulators, and “human or agent?” questions.

See stamp integration →

Developer integration

Sign-in in one element

The drop-in button handles the popup, the passkey, and the proof. Your backend verifies the presentation locally and uses the site-private ID as the account key. Need finer control? The SDK exposes the same flow with requiredAssurance: 'passkey'.

Passwordless sign-in, no registration or API key required

<script src="https://lemma.id/sdk/proof-verifier.js"></script>
<script src="https://lemma.id/sdk/lemma-signin.js"></script>

<lemma-signin site-id="app.example.com"></lemma-signin>

<script>
  document.querySelector('lemma-signin')
    .addEventListener('lemma-signin-success', async ({ detail }) => {
      // detail.presentation → verify server-side, then issue your session
      await fetch('/api/login', {
        method: 'POST',
        headers: { 'Content-Type': 'application/json' },
        body: JSON.stringify({ presentation: detail.presentation }),
      });
    });
</script>

View integration docs See the demo

Product boundaries

What lemma.id is not

Honest edges. It replaces the password and the signup form, not your whole account system.

Not a global identity

Every site gets its own ID for the same person. No shared identifier follows people across the web, by design.

Not a contact channel

You get an account key, not an email address. If your product needs to reach users, ask for contact info separately, and only when you actually need it.

Not bot detection

Finding suspicious behavior is still your fraud stack's job. lemma.id makes the consequence stick once you've decided, if you step up to human proofs.

Learn more

Trust & data model Integration docs Ticketing & presale About the approach

Add Sign in with lemma.id

Passwordless login your users can't lose and you don't have to protect. A script tag and a backend check, free.

Add to Your Site Watch Demo

Passwordless login.No user data to store.