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Rails 7 Passkey Demo

Introduction

All of this code was stolen from various places. webauthn is a Ruby gem which has a Rails 6.0.6 demo: webauthn-rails-demo-app. webauthn-json is also being used on the browser side.

What I’ve attempted to do is make a demo that uses passkeys and Rails 7 as stock as possible. I’m using importmap-rails and tailwindcss-rails (although I don’t claim ANY ability to design web pages.

Also note that I am not good at writing tests.

Basic Control Flow

There are two basic flows. One path is for a new unregistered user and the other path is for a previously registered user.

The database schema has a users table which has a has_many relationship to the credentials table. The key piece of data is the public_key kept in the credentials table.

An unregistered user will be directed to the registration/new URL where the registration ceremony will result in a new credential being created for the user with their public_key and other data. The final step is a call to sign_in(user) to store the new session that has been created along the way.

A registered user will be directed to the session/new URL which retrieves the users public key from their associated credentials and performs the log in ceremony and calls sign_in(user) assuming all goes well.

home/index is the root page for the application. HomeController is a subclass of AuthenticatedController which has a before_action of enforce_current_user. Any unauthenticated user is redirected to session/new. The session/new page has a link to registration/new for unregistered users.

Changes

webauthn-rails-demo-app had some errors. See Tangent to understand Webauthn. Here are changes from that project:

  • RegistrationsController#create
    1. An existing user by the same name is found if it exists. This will allow a user to have more than one method of logging in. For example, they could have a touch-id as well as a Yubikey.
    2. The hash that is sent via JSON contains more than the credentials. There are no magic values in the Javascript such as the path to the callback function.
    3. The Options for Credential Creation is created by WebAuthn::Credential#options_for_create which returns a WebAuthn::PublicKeyCredential::CreationOptions instance. The call to options_for_create is an options hash that contains the following keys specified in snake_case and are converted to camelBack via the to_json method of WebAuthn::PublicKeyCredential::CreationOptions.
      rp
      The Relying Party is added in by the options_for_create method by what is specified in config/initializers/webauthn.rb as documented in webauthn-ruby Configuration.
      user
      This is a hash with the following keys:
      id
      This is a randomized sequence of bytes that should come from WebAuthn.generate_user_id when the User model is created and preserved in the database. This is actually what the authentication ceremony looks at. The name and displayName are merely for human consumption.
      name
      Generally the “User name”
      display_name
      This is set equal to name if not explicitly supplied.
      timeout
      An optional number specifying the number of milliseconds to wait.
      attestation
      An optional attribute that is passed along unchanged.
      authenticator_selection
      An optional hash that is passed along unchanged. It too has snake_case keys which are converted to camelBack case. Authenticator Selection Criteria has these keys (given in snake_case):
      • authenticator_attachment
      • resident_key
      • require_resident_key
      • user_verification
      exclude_credentials
      An optional list (Array) of PublicKeyCredentialDescriptors to exclude from the create processing.
      exclude
      An optional more convenient method of creating exclude_credentials. If exclude_credentials is not specified, exclude can be specified as a list of strings and they are converted into tuples with id being set to the string value and type being set to “public”.
      pub_key_cred_params
      An optional list of hashes with type key which should have a value of “public” and an alg key which should have a value of an algorithm id such as -7 for the ES256 algorithm.
      algs
      An optional and more convenient method for creating the pub_key_cred_params list. A list of algorithm names such as “ES256” is given. Each name is transformed into a hash containing a key of type with a value of “public” and the corresponding algorithm’s id.
    4. The original code had a field for nickname. nickname appears four times in the WebAuthn specification such as here but it is an algorithmic conversion not something the user inputs. Thus nickname was removed from this implementation.
  • webauthn-json
    1. This implementation follows webauthn-json’s current recommendation of using browser ponyfill.
    2. The original implementation used a Stimulus controller feature_detection_controller to reveal a div if the browser could not support passkeys. The weakness is that if the feature detection completely fails, the div is not revealed leaving the user unaware that a problem has occurred.

      This implementation hides the form and shows the error div until the feature detection completes successfully and happily at which point the error div is hidden and the form is revealed. (This has not been implemented yet.)

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A demonstration Rails 7 project of how to use public WebAuthn (i.e. passkeys) for authentication

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