module ActiveRecord::TokenFor::ClassMethods

Defines the behavior of tokens generated for a specific purpose. A token can be generated by calling TokenFor#generate_token_for on a record. Later, that record can be fetched by calling find_by_token_for (or find_by_token_for!) with the same purpose and token.

Tokens are signed so that they are tamper-proof. Thus they can be exposed to outside world as, for example, password reset tokens.

By default, tokens do not expire. They can be configured to expire by specifying a duration via the expires_in option. The duration becomes part of the token’s signature, so changing the value of expires_in will automatically invalidate previously generated tokens.

A block may also be specified. When generating a token with TokenFor#generate_token_for, the block will be evaluated in the context of the record, and its return value will be embedded in the token as JSON. Later, when fetching the record with find_by_token_for, the block will be evaluated again in the context of the fetched record. If the two JSON values do not match, the token will be treated as invalid. Note that the value returned by the block should not contain sensitive information because it will be embedded in the token as human-readable plaintext JSON.

Examples

class User < ActiveRecord::Base
  has_secure_password

  generates_token_for :password_reset, expires_in: 15.minutes do
    # Last 10 characters of password salt, which changes when password is updated:
    password_salt&.last(10)
  end
end

user = User.first

token = user.generate_token_for(:password_reset)
User.find_by_token_for(:password_reset, token) # => user
# 16 minutes later...
User.find_by_token_for(:password_reset, token) # => nil

token = user.generate_token_for(:password_reset)
User.find_by_token_for(:password_reset, token) # => user
user.update!(password: "new password")
User.find_by_token_for(:password_reset, token) # => nil