WebAuthn :key:

Easily implement WebAuthn in your ruby/rails app

Gem Travis Join the chat at https://gitter.im/cedarcode/webauthn-ruby

What is WebAuthn?

Prerequisites

This gem will help your ruby server act as a conforming Relying-Party, in WebAuthn terminology. But for the Registration and Authentication ceremonies to work, you will also need

A conforming User Agent

Currently supporting Web Authentication API:

A conforming Authenticator

NOTE: Firefox states (Firefox 60 release notes) they only support USB FIDO2 or FIDO U2F enabled devices in their current implementation (version 60). It's up to the gem's user to verify user agent compatibility if any other device wants to be used as the authenticator component.

Installation

Add this line to your application's Gemfile:

gem 'webauthn'

And then execute:

$ bundle

Or install it yourself as:

$ gem install webauthn

Usage

NOTE: You can find a working example on how to use this gem in a Rails app in webauthn-rails-demo-app.

Registration

Initiation phase

credential_creation_options = WebAuthn.credential_creation_options

# Store the newly generated challenge somewhere so you can have it
# for the verification phase.
#
# You can read it from the resulting options:
credential_creation_options[:challenge]

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

Verification phase

# These should be ruby `String`s encoded as binary data, e.g. `Encoding:ASCII-8BIT`.
#
# If the user-agent is a web browser, you would use some encoding algorithm to send what
# `navigator.credentials.create` returned through the wire.
#
# Then you need to decode that data before passing it to the `#verify` method.
#
# E.g. in https://github.com/cedarcode/webauthn-rails-demo-app we use `Base64.strict_decode64`
# on the user-agent encoded data before calling `#verify`
attestation_object = "..."
client_data_json = "..."

attestation_response = WebAuthn::AuthenticatorAttestationResponse.new(
  attestation_object: attestation_object,
  client_data_json: client_data_json
)

# This value needs to match `window.location.origin` evaluated by
# the User Agent as part of the verification phase.
original_origin = "https://www.example.com"

begin
  attestation_response.verify(original_challenge, original_origin)

  # 1. Register the new user and
  # 2. Keep Credential ID and Credential Public Key under storage
  #    for future authentications
  #    Access by invoking:
  #      `attestation_response.credential.id`
  #      `attestation_response.credential.public_key`
rescue WebAuthn::VerificationError => e
  # Handle error
end

Authentication

Initiation phase

Assuming you have the previously stored Credential ID, now in variable credential_id

credential_request_options = WebAuthn.credential_request_options
credential_request_options[:allowCredentials] << { id: credential_id, type: "public-key" }

# Store the newly generated challenge somewhere so you can have it
# for the verification phase.
#
# You can read it from the resulting options:
credential_request_options[:challenge]

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

Verification phase

Assuming you have the previously stored Credential Public Key, now in variable credential_public_key

# These should be ruby `String`s encoded as binary data, e.g. `Encoding:ASCII-8BIT`.
#
# If the user-agent is a web browser, you would use some encoding algorithm to send what
# `navigator.credentials.get` returned through the wire.
#
# Then you need to decode that data before passing it to the `#verify` method.
#
# E.g. in https://github.com/cedarcode/webauthn-rails-demo-app we use `Base64.strict_decode64`
# on the user-agent encoded data before calling `#verify`
authenticator_data = "..."
client_data_json = "..."
signature = "..."

assertion_response = WebAuthn::AuthenticatorAssertionResponse.new(
  authenticator_data: authenticator_data,
  client_data_json: client_data_json,
  signature: signature
)

# This value needs to match `window.location.origin` evaluated by
# the User Agent as part of the verification phase.
original_origin = "https://www.example.com"

# This hash must have the id and its corresponding public key of the
# previously stored credential for the user that is attempting to sign in.
allowed_credential = {
  id: credential_id,
  public_key: credential_public_key
}

begin
  assertion_response.verify(original_challenge, original_origin, allowed_credentials: [allowed_credential])

  # Sign in the user
rescue WebAuthn::VerificationError => e
  # Handle error
end

Testing Your Integration

The Webauthn spec requires for data that is signed and authenticated. As a result, it can be difficult to create valid test authenticator data when testing your integration. webauthn-ruby exposes WebAuthn::FakeClient for you to use in your tests. Example usage can be found in webauthn-ruby/spec/webauthn/authenticator_assertion_response_spec.rb.

Development

After checking out the repo, run bin/setup to install dependencies. Then, run rake to run the tests and code-style checks. You can also run bin/console for an interactive prompt that will allow you to experiment.

Some tests require stubbing time with libfaketime in order to pass, otherwise they're skipped. You can install this library with your package manager. Follow libfaketime's instructions for your OS to preload the library before running the tests, and use the DONT_FAKE_MONOTONIC=1 FAKETIME_NO_CACHE=1 options. E.g. when installed via homebrew on macOS:

DYLD_INSERT_LIBRARIES=/usr/local/Cellar/libfaketime/2.9.7_1/lib/faketime/libfaketime.1.dylib DYLD_FORCE_FLAT_NAMESPACE=1 DONT_FAKE_MONOTONIC=1 FAKETIME_NO_CACHE=1 bundle exec rspec

To install this gem onto your local machine, run bundle exec rake install. To release a new version, update the version number in version.rb, and then run bundle exec rake release, which will create a git tag for the version, push git commits and tags, and push the .gem file to rubygems.org.

Commit message format

Each commit message follows the <type>: <message> format.

The "message" starts with lowercase and the "type" is one of:

  • build: Changes that affect the build system or external dependencies
  • ci: Changes to the CI configuration files and scripts
  • docs: Documentation only changes
  • feat: A new feature
  • fix: A bug fix
  • perf: A code change that improves performance
  • refactor: A code change that neither fixes a bug nor adds a feature
  • style: Changes that do not affect the meaning of the code (white-space, formatting, missing semi-colons, etc)
  • test: Adding missing tests or correcting existing tests

Inspired in a subset of Angular's Commit Message Guidelines.

Contributing

Bug reports and pull requests are welcome on GitHub at https://github.com/cedarcode/webauthn-ruby.

Security

If you have discovered a security bug, please send an email to security@cedarcode.com instead of posting to the GitHub issue tracker.

License

The gem is available as open source under the terms of the MIT License.