Anthropic-Cybersecurity-Skills/skills/implementing-passwordless-authentication-with-fido2/references/api-reference.md

API Reference: Implementing Passwordless Authentication with FIDO2

WebAuthn Registration Flow

// 1. Server generates challenge
const options = await navigator.credentials.create({
  publicKey: {
    challenge: new Uint8Array(32),
    rp: { name: "Example Corp", id: "example.com" },
    user: { id: userId, name: "user@example.com", displayName: "User" },
    pubKeyCredParams: [
      { type: "public-key", alg: -7 },   // ES256
      { type: "public-key", alg: -257 }, // RS256
    ],
    authenticatorSelection: {
      authenticatorAttachment: "platform",  // or "cross-platform"
      residentKey: "required",              // for passkeys
      userVerification: "required",
    },
    attestation: "direct",
  }
});

WebAuthn Authentication Flow

const assertion = await navigator.credentials.get({
  publicKey: {
    challenge: serverChallenge,
    rpId: "example.com",
    allowCredentials: [],  // empty for discoverable credentials (passkeys)
    userVerification: "required",
  }
});

python-fido2 Server Library

from fido2.server import Fido2Server
from fido2.webauthn import PublicKeyCredentialRpEntity

rp = PublicKeyCredentialRpEntity(id="example.com", name="Example")
server = Fido2Server(rp)

# Registration
registration_data, state = server.register_begin(user, credentials)
auth_data = server.register_complete(state, response)

# Authentication
request_data, state = server.authenticate_begin(credentials)
server.authenticate_complete(state, credentials, credential_id, client_data, auth_data, signature)

FIDO2 Authenticator Types

Type	Example	Attachment	Passkey Support
Platform	Windows Hello, Touch ID	platform	Yes
Roaming	YubiKey, Titan Key	cross-platform	Yes (FIDO2)
Software	1Password, iCloud Keychain	platform	Yes

COSE Algorithm Identifiers

COSE ID	Algorithm	Use
-7	ES256 (P-256)	Preferred for FIDO2
-257	RS256	Legacy compatibility
-8	EdDSA (Ed25519)	Strong, compact
-35	ES384 (P-384)	Higher security

NIST SP 800-63B AAL Levels

Level	Requirements	FIDO2 Mapping
AAL1	Single factor	Not applicable
AAL2	Two factors	FIDO2 + PIN/biometric
AAL3	Hardware crypto + verifier impersonation resistance	FIDO2 hardware key

Azure AD FIDO2 Configuration

# Enable FIDO2 in Azure AD
Set-MgBetaPolicyAuthenticationMethodPolicyAuthenticationMethodConfiguration `
  -AuthenticationMethodConfigurationId "fido2" `
  -State "enabled" `
  -AdditionalProperties @{
    isSelfServiceRegistrationAllowed = $true
    isAttestationEnforced = $true
  }

References

• WebAuthn Spec: https://www.w3.org/TR/webauthn-3/
• FIDO Alliance: https://fidoalliance.org/specifications/
• NIST SP 800-63B: https://pages.nist.gov/800-63-3/sp800-63b.html
• python-fido2: https://github.com/Yubico/python-fido2