Add a `U2fRegistrations` table/model.

- To hold registrations from U2F devices, and to authenticate them.
- Previously, `User#two_factor_enabled` was aliased to the
  `otp_required_for_login` column on `users`.
- This commit changes things a bit:
    - `User#two_factor_enabled` is not a method anymore
    - `User#two_factor_enabled?` checks both the
      `otp_required_for_login` column, as well as `U2fRegistration`s
    - Change all instances of `User#two_factor_enabled` to
      `User#two_factor_enabled?`
- Add the `u2f` gem, and implement registration/authentication at the
  model level.

1 files changed, 40 insertions, 0 deletions

diff --git a/app/models/u2f_registration.rb b/app/models/u2f_registration.rb
new file mode 100644
index 00000000000..00b19686d48
--- /dev/null
+++ b/app/models/u2f_registration.rb
@@ -0,0 +1,40 @@
+# Registration information for U2F (universal 2nd factor) devices, like Yubikeys
+
+class U2fRegistration < ActiveRecord::Base
+  belongs_to :user
+
+  def self.register(user, app_id, json_response, challenges)
+    u2f = U2F::U2F.new(app_id)
+    registration = self.new
+
+    begin
+      response = U2F::RegisterResponse.load_from_json(json_response)
+      registration_data = u2f.register!(challenges, response)
+      registration.update(certificate: registration_data.certificate,
+                          key_handle: registration_data.key_handle,
+                          public_key: registration_data.public_key,
+                          counter: registration_data.counter,
+                          user: user)
+    rescue JSON::ParserError, NoMethodError, ArgumentError
+      registration.errors.add(:base, 'Your U2F device did not send a valid JSON response.')
+    rescue U2F::Error => e
+      registration.errors.add(:base, e.message)
+    end
+
+    registration
+  end
+
+  def self.authenticate(user, app_id, json_response, challenges)
+    response = U2F::SignResponse.load_from_json(json_response)
+    registration = user.u2f_registrations.find_by_key_handle(response.key_handle)
+    u2f = U2F::U2F.new(app_id)
+
+    if registration
+      u2f.authenticate!(challenges, response, Base64.decode64(registration.public_key), registration.counter)
+      registration.update(counter: response.counter)
+      true
+    end
+  rescue JSON::ParserError, NoMethodError, ArgumentError, U2F::Error
+    false
+  end
+end