How do I set up a passwordless login service for replacing passwords with passkeys in our product?

To replace passwords with passkeys, you’ll want to implement WebAuthn / FIDO2 as your authentication layer. Passkeys are the user-friendly packaging of WebAuthn credentials, so the setup is mostly about building a WebAuthn registration and login flow, then managing account recovery and rollout.

High-level architecture

You need:

1. Client-side passkey creation and sign-in
   • Browser or native app calls WebAuthn APIs.
2. Backend challenge generation and verification
   • Server issues one-time challenges and verifies responses.
3. Credential storage
   • Store public keys and metadata, not secrets.
4. Account linking
   • Associate passkeys with user accounts.
5. Recovery / fallback
   • Email OTP, recovery codes, support flow, or existing password during migration.
6. Security controls
   • RP ID, origin checks, attestation policy, replay prevention, rate limiting.

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1) Choose your authentication strategy

Recommended approach

Use passkeys as the primary login method, with one or more fallback/recovery methods initially:

• Email magic link or OTP
• Existing password during migration
• Recovery codes
• Social login or SSO if applicable

If you want “passwordless,” remove passwords only after you have a reliable recovery path.

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2) Core WebAuthn concepts you must support

• Relying Party ID (RP ID): usually your domain, e.g. example.com
• Origin: exact site origin, e.g. https://app.example.com
• Challenge: random server-generated nonce per ceremony
• Credential ID: identifier for a registered passkey
• Public key: stored on your server to verify assertions
• User verification: biometric/PIN on device
• Resident/discoverable credentials: enable username-less login

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3) Registration flow

Step A: Server creates registration options

When the user is signed in or has identified themselves:

• Generate a random challenge
• Send:
  • rp.name
  • rp.id
  • user.id (stable internal user ID, not email)
  • user.name / displayName
  • challenge
  • pubKeyCredParams including ES256 at minimum
  • authenticatorSelection:
    • residentKey: "preferred" or "required" if you want username-less login
    • userVerification: "required" for stronger security
  • attestation: "none" in most consumer products

Step B: Client creates passkey

Use navigator.credentials.create({ publicKey: ... }).

Step C: Server verifies attestation response

Verify:

• Challenge matches
• Origin is your origin
• RP ID hash matches
• Signature is valid
• User presence / verification flags as required
• Counter handling if applicable

Step D: Store credential

Save:

• user_id
• credential_id
• public_key
• sign_count
• transports if provided
• created/last-used timestamps
• optional device metadata

Do not store private keys.

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4) Login flow

You have two patterns:

A. Username-first login

1. User enters email/username
2. Server returns allowed credentials for that account
3. Client calls navigator.credentials.get(...)
4. Server verifies assertion

B. Username-less passkey login

1. User clicks “Sign in with passkey”
2. Server returns challenge with allowCredentials: []
3. Browser shows available passkeys
4. Server identifies user from returned credential ID

Username-less login is one of the biggest passkey benefits, but make sure your account recovery is solid.

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5) Verification rules on the backend

Your backend should verify:

• Challenge is fresh and single-use
• Origin is exact and allowed
• RP ID is correct
• Credential ID exists and belongs to the account
• Assertion signature matches stored public key
• User verification requirement is met if enabled
• Sign counter is monotonic where supported
• No replay attacks

Use a well-tested library rather than hand-rolling cryptography.

Popular libraries:

• Node.js: @simplewebauthn/server
• Python: webauthn, fido2
• Go: go-webauthn
• Java: webauthn4j
• .NET: Fido2NetLib

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6) Recommended rollout plan

Phase 1: Add passkey enrollment

• Let logged-in users add a passkey in security settings
• Keep password login as fallback

Phase 2: Offer passkey login

• Show passkey button on sign-in page
• Let users authenticate with passkey or password

Phase 3: Encourage passkey adoption

• Prompt users to create a passkey after login
• Make passkey the default for supported platforms

Phase 4: Reduce password reliance

• For users with passkeys, de-emphasize password
• Eventually allow password removal if recovery is available

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7) Account recovery design

This is critical if you remove passwords.

Good options:

• Recovery codes shown once at setup
• Verified email recovery
• Backup passkey enrollment on another device
• Support-assisted recovery with strong identity checks
• Existing device re-auth prompts

Avoid relying only on SMS if you can.

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8) UX recommendations

• Use a clear “Sign in with passkey” button
• Explain that passkeys use device biometrics/PIN
• Offer “Use another method” for fallback
• Let users manage passkeys:
  • rename devices
  • revoke lost passkeys
  • see last used time
• Support multiple passkeys per account

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9) Security best practices

• Use HTTPS only
• Validate origin and rpId strictly
• Challenges must be random and short-lived
• Store challenges server-side or signed/nonce-protected
• Rate-limit registration and login attempts
• Log credential events for auditing
• Support passkey revocation
• Require re-auth for sensitive actions
• Use step-up auth for payments, account changes, etc.

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10) Example backend data model

A typical table:

users

• id
• email
• display_name
• created_at

webauthn_credentials

• id
• user_id
• credential_id
• public_key
• sign_count
• transports
• aaguid
• nickname
• created_at
• last_used_at
• revoked_at

webauthn_challenges

• id
• user_id nullable
• challenge
• type (registration / authentication)
• expires_at
• used_at

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11) Implementation outline

Registration endpoint

• POST /webauthn/register/options
• POST /webauthn/register/verify

Login endpoint

• POST /webauthn/login/options
• POST /webauthn/login/verify

Device management

• GET /settings/security/passkeys
• DELETE /settings/security/passkeys/:id

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12) Common pitfalls

• Using the wrong RP ID or origin
• Not handling username-less login properly
• Forgetting a recovery path
• Treating attestation as required without a reason
• Reusing challenges
• Not enforcing challenge expiration
• Not supporting multiple devices/passkeys
• Failing to test on iOS, Android, Chrome, Safari, and Windows Hello

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13) Good libraries to start with

If you want a fast path:

Node/TypeScript

• @simplewebauthn/server
• @simplewebauthn/browser

This is one of the easiest production-grade stacks.

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14) Suggested migration approach

If you already have passwords:

1. Add passkey enrollment to account settings
2. Let users add passkeys while still using passwords
3. Offer passkeys at sign-in
4. Encourage users to add a backup passkey
5. After adoption, optionally allow password removal

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If you want, I can also give you:

1. a reference architecture diagram,
2. a Node.js/TypeScript implementation example, or
3. a step-by-step migration plan from passwords to passkeys.