FEATURE: Webauthn authenticator management with 2FA login (Security Keys) (#8099)

Adds 2 factor authentication method via second factor security keys over [web authn](https://developer.mozilla.org/en-US/docs/Web/API/Web_Authentication_API).

Allows a user to authenticate a second factor on login, login-via-email, admin-login, and change password routes. Adds registration area within existing user second factor preferences to register multiple security keys. Supports both external (yubikey) and built-in (macOS/android fingerprint readers).

db/migrate/20190904104533_create_user_security_keys.rb

@@ -0,0 +1,26 @@
+# frozen_string_literal: true
+
+class CreateUserSecurityKeys < ActiveRecord::Migration[5.2]
+  def up
+    create_table :user_security_keys do |t|
+      t.references :user, null: false, index: true, foreign_key: true
+      t.string :credential_id, null: false
+      t.string :public_key, null: false, index: true
+      t.integer :factor_type, null: false, default: 0, index: true
+      t.boolean :enabled, null: false, default: true
+      t.string :name, null: false
+      t.datetime :last_used
+
+      t.timestamps
+    end
+
+    add_index :user_security_keys, :credential_id, unique: true
+    add_index :user_security_keys, :last_used
+  end
+
+  def down
+    if table_exists?(:user_security_keys)
+      drop_table(:user_security_keys)
+    end
+  end
+end

db/migrate/20190908233325_add_secure_identifier_column_to_users.rb

@@ -0,0 +1,8 @@
+# frozen_string_literal: true
+
+class AddSecureIdentifierColumnToUsers < ActiveRecord::Migration[5.2]
+  def change
+    add_column :users, :secure_identifier, :string
+    add_index :users, :secure_identifier, unique: true
+  end
+end

db/migrate/20190917100006_add_enabled_index_to_user_security_key.rb

@@ -0,0 +1,7 @@
+# frozen_string_literal: true
+
+class AddEnabledIndexToUserSecurityKey < ActiveRecord::Migration[6.0]
+  def change
+    add_index :user_security_keys, [:factor_type, :enabled]
+  end
+end