Passkeys / WebAuthn (FIDO2)
Provides the FIDO2/WebAuthn standard for phishing-resistant, passwordless authentication using device-bound cryptographic credentials, implemented via libraries such as SimpleWebAuthn (JS) and py_webauthn (Python).
Score Breakdown
⚙ Agent Friendliness
🔒 Security
Private keys never leave the authenticator device; HTTPS required by spec; resistant to phishing and credential stuffing
⚡ Reliability
Best When
You need strong, phishing-resistant human authentication as a gate before an agent takes sensitive actions on behalf of that user.
Avoid When
Your users are non-human service accounts, or you need to authenticate in headless environments without any user-facing browser or device.
Use Cases
- • Register and authenticate human users into an agent-orchestrated application without passwords or SMS OTP
- • Validate WebAuthn assertion responses server-side before granting an agent access token tied to a verified human session
- • Implement step-up authentication prompts within an agentic workflow when a high-risk action requires fresh user verification
- • Store and retrieve passkey credential metadata (credential ID, public key, sign count) in your user database for ongoing authentication
- • Enforce hardware-bound authentication for admin-level operations that an AI agent must not execute without explicit human approval
Not For
- • Machine-to-machine or service account authentication — passkeys require a human with a FIDO2-capable device
- • Environments where users lack modern browsers, OS authenticators, or hardware security keys
- • Replacing authorization logic — WebAuthn proves identity only; what the authenticated user may do requires a separate authz layer
Interface
Authentication
WebAuthn is itself the authentication standard; individual library implementations require no separate auth credentials
Pricing
The WebAuthn specification and all major reference libraries are free and open source; hosting costs are your own infrastructure
Agent Metadata
Known Gotchas
- ⚠ Relying Party ID (rpID) must exactly match the origin domain; mismatches silently fail with a cryptographic verification error that is hard to distinguish from user error
- ⚠ Challenge values must be generated server-side, stored in session, and validated exactly once — stateless agents must persist challenge state between ceremony steps
- ⚠ Sign counter validation is required by spec but many implementations make it optional; skipping it defeats replay attack protection
- ⚠ CBOR encoding of authenticator data requires a dedicated library (cbor2, etc.) — agents that try to parse raw bytes manually will encounter subtle decode bugs
- ⚠ iOS and Android passkey syncing via iCloud Keychain or Google Password Manager changes the expected aaguid, breaking attestation checks that rely on hardware identity
Alternatives
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Scores are editorial opinions as of 2026-03-07.