Migrate passwords from legacy systems to Devise

user.rb

# updated variant of older solution: 
# http://www.davidverhasselt.com/2012/05/13/how-to-migrate-passwords-from-legacy-systems-to-devise

class User < ActiveRecord::Base
  
  # ...
  
  def valid_password?(password)
    if legacy_password?
      # Use Devise's secure_compare to avoid timing attacks
      return false unless super User.legacy_password(password)
      self.attributes = { password: password, password_confirmation: password, legacy_password: false }
      self.save!
    end
    super password
  end
 
  # Put your legacy password hashing method here
  def self.legacy_password(password)
    return Digest::MD5.hexdigest("#{password}-salty-herring");
  end
end