gem 'webauthn'

WebAuthn.configure do |config|
  # This value needs to match `window.location.origin` evaluated by
  # the User Agent during registration and authentication ceremonies.
  config.origin = "https://auth.example.com"

  # Relying Party name for display purposes
  config.rp_name = "Example Inc."

  # Optionally configure a client timeout hint, in milliseconds.
  # This hint specifies how long the browser should wait for any
  # interaction with the user.
  # This hint may be overridden by the browser.
  # https://www.w3.org/TR/webauthn/#dom-publickeycredentialcreationoptions-timeout
  # config.credential_options_timeout = 120_000

  # You can optionally specify a different Relying Party ID
  # (https://www.w3.org/TR/webauthn/#relying-party-identifier)
  # if it differs from the default one.
  #
  # In this case the default would be "auth.example.com", but you can set it to
  # the suffix "example.com"
  #
  # config.rp_id = "example.com"

  # Configure preferred binary-to-text encoding scheme. This should match the encoding scheme
  # used in your client-side (user agent) code before sending the credential to the server.
  # Supported values: `:base64url` (default), `:base64` or `false` to disable all encoding.
  #
  # config.encoding = :base64url

  # Possible values: "ES256", "ES384", "ES512", "PS256", "PS384", "PS512", "RS256", "RS384", "RS512", "RS1"
  # Default: ["ES256", "PS256", "RS256"]
  #
  # config.algorithms << "ES384"
end

# Generate and store the WebAuthn User ID the first time the user registers a credential
if !user.webauthn_id
  user.update!(webauthn_id: WebAuthn.generate_user_id)
end

options = WebAuthn::Credential.options_for_create(
  user: { id: user.webauthn_id, name: user.name },
  exclude: user.credentials.map { |c| c.webauthn_id }
)

# Store the newly generated challenge somewhere so you can have it
# for the verification phase.
session[:creation_challenge] = options.challenge

# Send `options` back to the browser, so that they can be used
# to call `navigator.credentials.create({ "publicKey": options })`
#
# You can call `options.as_json` to get a ruby hash with a JSON representation if needed.

# If inside a Rails controller, `render json: options` will just work.
# I.e. it will encode and convert the options to JSON automatically.

# For your frontend code, you might find @github/webauthn-json npm package useful.
# Especially for handling the necessary decoding of the options, and sending the
# `PublicKeyCredential` object back to the server.

# Assuming you're using @github/webauthn-json package to send the `PublicKeyCredential` object back
# in params[:publicKeyCredential]:
webauthn_credential = WebAuthn::Credential.from_create(params[:publicKeyCredential])

begin
  webauthn_credential.verify(session[:creation_challenge])

  # Store Credential ID, Credential Public Key and Sign Count for future authentications
  user.credentials.create!(
    webauthn_id: webauthn_credential.id,
    public_key: webauthn_credential.public_key,
    sign_count: webauthn_credential.sign_count
  )
rescue WebAuthn::Error => e
  # Handle error
end

options = WebAuthn::Credential.options_for_get(allow: user.credentials.map { |c| c.webauthn_id })

# Store the newly generated challenge somewhere so you can have it
# for the verification phase.
session[:authentication_challenge] = options.challenge

# Send `options` back to the browser, so that they can be used
# to call `navigator.credentials.get({ "publicKey": options })`

# You can call `options.as_json` to get a ruby hash with a JSON representation if needed.

# If inside a Rails controller, `render json: options` will just work.
# I.e. it will encode and convert the options to JSON automatically.

# For your frontend code, you might find @github/webauthn-json npm package useful.
# Especially for handling the necessary decoding of the options, and sending the
# `PublicKeyCredential` object back to the server.

# Assuming you're using @github/webauthn-json package to send the `PublicKeyCredential` object back
# in params[:publicKeyCredential]:
webauthn_credential = WebAuthn::Credential.from_get(params[:publicKeyCredential])

stored_credential = user.credentials.find_by(webauthn_id: webauthn_credential.id)

begin
  webauthn_credential.verify(
    session[:authentication_challenge],
    public_key: stored_credential.public_key,
    sign_count: stored_credential.sign_count
  )

  # Update the stored credential sign count with the value from `webauthn_credential.sign_count`
  stored_credential.update!(sign_count: webauthn_credential.sign_count)

  # Continue with successful sign in or 2FA verification...

rescue WebAuthn::SignCountVerificationError => e
  # Cryptographic verification of the authenticator data succeeded, but the signature counter was less then or equal
  # to the stored value. This can have several reasons and depending on your risk tolerance you can choose to fail or
  # pass authentication. For more information see https://www.w3.org/TR/webauthn/#sign-counter
rescue WebAuthn::Error => e
  # Handle error
end

WebAuthn.generate_user_id # "lWoMZTGf_ml2RoY5qPwbwrkxrvTqWjGOxEoYBgxft3zG-LlrICvE-y8bxFi06zMyIOyNsJoWx4Fa2TOqoRmnxA"

creation_options = WebAuthn::Credential.options_for_create(
  user: { id: user.webauthn_id, name: user.name }
  exclude: user.credentials.map { |c| c.webauthn_id }
)

# Store the newly generated challenge somewhere so you can have it
# for the verification phase.
session[:creation_challenge] = creation_options.challenge

# Send `creation_options` back to the browser, so that they can be used
# to call `navigator.credentials.create({ "publicKey": creationOptions })`
#
# You can call `creation_options.as_json` to get a ruby hash with a JSON representation if needed.

# If inside a Rails controller, `render json: creation_options` will just work.
# I.e. it will encode and convert the options to JSON automatically.

request_options = WebAuthn::Credential.options_for_get(allow: user.credentials.map { |c| c.webauthn_id })

# Store the newly generated challenge somewhere so you can have it
# for the verification phase.
session[:authentication_challenge] = request_options.challenge

# Send `request_options` back to the browser, so that they can be used
# to call `navigator.credentials.get({ "publicKey": requestOptions })`

# You can call `request_options.as_json` to get a ruby hash with a JSON representation if needed.

# If inside a Rails controller, `render json: request_options` will just work.
# I.e. it will encode and convert the options to JSON automatically.

credential_with_attestation = WebAuthn::Credential.from_create(params[:publicKeyCredential])

credential_with_assertion = WebAuthn::Credential.from_get(params[:publicKeyCredential])

credential_with_attestation.verify(session[:creation_challenge])

credential_with_assertion.verify(
  session[:authentication_challenge],
  public_key: stored_credential.public_key,
  sign_count: stored_credential.sign_count
)