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)
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March 29, 2010
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Wrong example

In the authentication filter example above, the time condition should be reversed: we only want to find the user if time is still in the future (because it’s the valid-until time).

So the example should look like this:

id, time = @verifier.verify(cookies[:remember_me])
if time > Time.now
  self.current_user = User.find(id)
August 14, 2011
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Security issue

One thing to note about the code above is that it could have a security issue. If the user changes his/her password, the authentication token should expire. Hence, in a production scenario you should put in the password salt or something to allow the token to become invalidated.

May 4, 2014
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In regards to @aamer’s comment on including the password salt this is a bad idea. `ActiveSupport::MessageVerifier` is NOT encrypted so:

verifier = ActiveSupport::MessageVerifier.new('secret')
id = 'id'
salt = 'salt'
verifier.generate("#{id}-#{salt}") # "BAhJIgxpZC1zYWx0BjoGRVQ=--c880254708d18ce4a686bcd96a25cf0d2117e1e0"

Base64.decode64(token.split("--").first) # "...id-salt..."

Note how the salt and id are both exposed! Instead a different token (reset_passowrd_token) should be used.