Class: Capybara::Simulated::WebauthnState

Inherits:
Object
  • Object
show all
Defined in:
lib/capybara/simulated/webauthn_state.rb

Overview

Per-Browser virtual WebAuthn authenticator state. Mirrors the subset of the WebAuthn Level 2 spec real apps (Discourse’s security key + passkey flows) exercise: ES256 keys, fmt=“none” attestation, AAGUID per authenticator, excludeCredentials + userVerification + resident-key enforcement, and the CDP ‘WebAuthn.*` surface that tests drive through `cdp.with_virtual_authenticator`.

Defined Under Namespace

Classes: CborBytes, Credential, Error

Constant Summary collapse

ES256_ALG = 
-7
P256_CRV = 
1
KTY_EC2 = 
2
FLAG_UP =

Flags byte in authenticator data (rfc8152 / WebAuthn level 2).

0x01
FLAG_UV =

User Present

0x04
FLAG_BE =

User Verified

0x08
FLAG_BS =

Backup Eligible

0x10
FLAG_AT =

Backup State

0x40
FLAG_ED =

Attested credential data included

0x80
DEFAULT_AAGUID =

Extension data included

("\x00" * 16).b.freeze

Instance Method Summary collapse

Constructor Details

#initialize ⇒ WebauthnState

Returns a new instance of WebauthnState.



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# File 'lib/capybara/simulated/webauthn_state.rb', line 46

def initialize
  @authenticators = {}
  @next_handle    = 1
end

Instance Method Details

#add_credential(handle, credential) ⇒ Object 



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# File 'lib/capybara/simulated/webauthn_state.rb', line 67

def add_credential(handle, credential)
  auth = @authenticators[handle.to_s] or return
  raw_id = Base64.urlsafe_decode64(credential['credentialId'].to_s)
  priv   = OpenSSL::PKey::EC.new(Base64.urlsafe_decode64(credential['privateKey'].to_s))
  auth[:credentials][raw_id] = Credential.new(
    raw_id:      raw_id,
    private_key: priv,
    rp_id:       credential['rpId'].to_s,
    sign_count:  credential['signCount'].to_i,
    resident:    !!credential['isResidentCredential'],
    user_handle: credential['userHandle'] ? Base64.urlsafe_decode64(credential['userHandle'].to_s) : nil
  )
  raw_id
end

#add_virtual_authenticator(options) ⇒ Object 



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# File 'lib/capybara/simulated/webauthn_state.rb', line 51

def add_virtual_authenticator(options)
  opts = (options || {}).transform_keys(&:to_s)
  handle = "csim-auth-#{@next_handle}"
  @next_handle += 1
  @authenticators[handle] = {
    options:     opts,
    credentials: {},
    aaguid:      DEFAULT_AAGUID
  }
  handle
end

#create(json) ⇒ Object 



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# File 'lib/capybara/simulated/webauthn_state.rb', line 105

def create(json)
  req  = JSON.parse(json.to_s)
  auth = pick_authenticator_for_create(req) or
         raise Error.new('NotAllowedError', 'no compatible virtual authenticator')

  rp_id     = req.dig('rp', 'id').to_s
  rp_id     = host_from_origin(req['origin']) if rp_id.empty?
  challenge = Base64.urlsafe_decode64(req['challenge'].to_s)
  user_id   = Base64.urlsafe_decode64(req.dig('user', 'id').to_s)
  opts      = auth[:options]

  unless (req['pubKeyCredParams'] || []).any? {|p| p['alg'].to_i == ES256_ALG }
    raise Error.new('NotSupportedError', 'no supported pubKeyCredParam (ES256 only)')
  end

  (req['excludeCredentials'] || []).each do |c|
    if auth[:credentials][Base64.urlsafe_decode64(c['id'].to_s)]
      raise Error.new('InvalidStateError', 'credential already registered on this authenticator')
    end
  end

  sel    = req['authenticatorSelection'] || {}
  uv_req = sel['userVerification']
  require_resident = %w[required preferred].include?(sel['residentKey']) ||
                     sel['requireResidentKey']
  if require_resident && !opts['hasResidentKey']
    raise Error.new('ConstraintError', 'resident-key required but authenticator does not support it')
  end
  if uv_req == 'required' && !user_verified?(opts)
    raise Error.new('NotAllowedError', 'user verification required but not performed')
  end

  key     = OpenSSL::PKey::EC.generate('prime256v1')
  raw_id  = SecureRandom.random_bytes(32)
  is_resident = !!(opts['hasResidentKey'] && require_resident)
  flags   = FLAG_UP | FLAG_AT
  flags  |= FLAG_UV if user_verified?(opts)
  # BE/BS mark the credential as syncable — clients use this to
  # decide whether to surface "passkey" UX vs "this device only".
  flags  |= (FLAG_BE | FLAG_BS) if opts['hasResidentKey'] && opts['hasUserVerification']

  auth_data = OpenSSL::Digest::SHA256.digest(rp_id) +
              [flags].pack('C') +
              [0].pack('N') +
              auth[:aaguid] +
              [raw_id.bytesize].pack('n') +
              raw_id +
              cose_ec2_pubkey(key)

  attestation_object = cbor_encode(
    'fmt'      => 'none',
    'attStmt'  => {},
    'authData' => CborBytes.new(auth_data)
  )

  client_data = JSON.dump(
    type:        'webauthn.create',
    challenge:   Base64.urlsafe_encode64(challenge.b, padding: false),
    origin:      req['origin'].to_s,
    crossOrigin: false
  )

  auth[:credentials][raw_id] = Credential.new(
    raw_id:      raw_id,
    private_key: key,
    rp_id:       rp_id,
    sign_count:  0,
    resident:    is_resident || !!opts['hasResidentKey'],
    user_handle: user_id
  )

  {
    'credentialId'      => Base64.urlsafe_encode64(raw_id.b, padding: false),
    'clientDataJSON'    => Base64.urlsafe_encode64(client_data.b, padding: false),
    'attestationObject' => Base64.urlsafe_encode64(attestation_object.b, padding: false)
  }
end

#get(json) ⇒ Object

Raises:



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# File 'lib/capybara/simulated/webauthn_state.rb', line 183

def get(json)
  req  = JSON.parse(json.to_s)

  rp_id     = req['rpId'].to_s
  rp_id     = host_from_origin(req['origin']) if rp_id.empty?
  challenge = Base64.urlsafe_decode64(req['challenge'].to_s)
  allow     = (req['allowCredentials'] || []).map {|c| Base64.urlsafe_decode64(c['id'].to_s) }
  uv_req    = req['userVerification']

  pick = pick_credential_for_get(rp_id, allow)
  raise Error.new('NotAllowedError', 'no matching credential') unless pick
  auth, cred = pick
  opts = auth[:options]

  if uv_req == 'required' && !user_verified?(opts)
    raise Error.new('NotAllowedError', 'user verification required but not performed')
  end

  cred.sign_count += 1

  flags  = FLAG_UP
  flags |= FLAG_UV if user_verified?(opts)
  flags |= (FLAG_BE | FLAG_BS) if cred.resident && opts['hasUserVerification']
  auth_data = OpenSSL::Digest::SHA256.digest(rp_id) +
              [flags].pack('C') +
              [cred.sign_count].pack('N')

  client_data = JSON.dump(
    type:        'webauthn.get',
    challenge:   Base64.urlsafe_encode64(challenge.b, padding: false),
    origin:      req['origin'].to_s,
    crossOrigin: false
  )

  signed_payload = auth_data + OpenSSL::Digest::SHA256.digest(client_data)
  signature      = cred.private_key.sign(OpenSSL::Digest::SHA256.new, signed_payload)

  # WebAuthn level 2: userHandle is only returned for resident
  # (discoverable) credentials. Real authenticators don't surface
  # the bound user for plain server-side credentials.
  user_handle_out = cred.resident && cred.user_handle && !cred.user_handle.empty? ?
                    Base64.urlsafe_encode64(cred.user_handle.b, padding: false) : nil

  {
    'credentialId'      => Base64.urlsafe_encode64(cred.raw_id.b, padding: false),
    'clientDataJSON'    => Base64.urlsafe_encode64(client_data.b, padding: false),
    'authenticatorData' => Base64.urlsafe_encode64(auth_data.b, padding: false),
    'signature'         => Base64.urlsafe_encode64(signature.b, padding: false),
    'userHandle'        => user_handle_out
  }
end

#get_credentials(handle) ⇒ Object 



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# File 'lib/capybara/simulated/webauthn_state.rb', line 87

def get_credentials(handle)
  auth = @authenticators[handle.to_s] or return []
  auth[:credentials].values.map {|c|
    {
      'credentialId'         => Base64.urlsafe_encode64(c.raw_id.b, padding: false),
      'rpId'                 => c.rp_id,
      'isResidentCredential' => c.resident,
      'signCount'            => c.sign_count,
      'userHandle'           => c.user_handle ? Base64.urlsafe_encode64(c.user_handle.b, padding: false) : nil
    }
  }
end

#remove_credential(handle, credential_id_b64) ⇒ Object 



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# File 'lib/capybara/simulated/webauthn_state.rb', line 82

def remove_credential(handle, credential_id_b64)
  auth = @authenticators[handle.to_s] or return
  auth[:credentials].delete(Base64.urlsafe_decode64(credential_id_b64.to_s))
end

#remove_virtual_authenticator(handle) ⇒ Object 



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# File 'lib/capybara/simulated/webauthn_state.rb', line 63

def remove_virtual_authenticator(handle)
  @authenticators.delete(handle.to_s)
end

#set_user_verified(handle, verified) ⇒ Object 



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# File 'lib/capybara/simulated/webauthn_state.rb', line 100

def set_user_verified(handle, verified)
  auth = @authenticators[handle.to_s] or return
  auth[:options]['isUserVerified'] = !!verified
end