MessageVerifier makes it easy to generate and verify messages which are signed to prevent tampering.

This is useful for cases like remember-me tokens and auto-unsubscribe links where the session store isn’t suitable or available.

Remember Me:

cookies[:remember_me] = @verifier.generate([@user.id, 2.weeks.from_now])

In the authentication filter:

id, time = @verifier.verify(cookies[:remember_me])
if time < Time.now
  self.current_user = User.find(id)
end
Methods
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Classes and Modules
Class Public methods
new(secret, digest = 'SHA1')

Source: show | on GitHub 

# File activesupport/lib/active_support/message_verifier.rb, line 24
def initialize(secret, digest = 'SHA1')
  @secret = secret
  @digest = digest
end
Instance Public methods
generate(value)

Source: show | on GitHub 

# File activesupport/lib/active_support/message_verifier.rb, line 40
def generate(value)
  data = ActiveSupport::Base64.encode64s(Marshal.dump(value))
  "#{data}--#{generate_digest(data)}"
end
verify(signed_message)

Source: show | on GitHub 

# File activesupport/lib/active_support/message_verifier.rb, line 29
def verify(signed_message)
  raise InvalidSignature if signed_message.blank?

  data, digest = signed_message.split("--")
  if data.present? && digest.present? && secure_compare(digest, generate_digest(data))
    Marshal.load(ActiveSupport::Base64.decode64(data))
  else
    raise InvalidSignature
  end
end