Add Token model

app/models/token.rb

@@ -0,0 +1,38 @@
+class Token < ApplicationRecord
+  # A Token contains some information that can be used as an alternative way to
+  # authenticate a user, typically instead of a username/password combination.
+  #
+  # At least the following types of tokens will exist:
+  #  - Account confirmation tokens, sent to the user when their account is
+  #    created (to verify their email address)
+  #  - Password reset tokens
+  #  - API authentication tokens
+  #
+  # @!attribute token
+  #  @return [String]
+  #    a unique token, that allows the holder to perform some action.
+  #
+  # @!attribute expires
+  #   @return [DateTime]
+  #     when the token will expire (and will no longer be usable).
+  #
+  # @!attribute tokentype
+  #   @return [String]
+  #     what action the token allows the holder to perform. Use the hash
+  #     Token::TYPES instead of comparing directly!
+  #
+  # @!attribute user
+  #   @return [User]
+  #     what user the token allows the holder to authenticate as.
+
+  TYPES = {
+    password_reset:       'pw_reset',
+    account_confirmation: 'confirm',
+    api_authentication:   'api'
+  }
+
+  validates :token, uniqueness: true, presence: true
+  validates :user, presence: true
+
+  belongs_to :user
+end