module ActiveModel::SecurePassword::InstanceMethodsOnActivation

def authenticate(unencrypted_password)

user.authenticate('mUc3m00RsqyRe') # => user
user.authenticate('notright') # => false
user.save
user = User.new(name: 'david', password: 'mUc3m00RsqyRe')

end
has_secure_password validations: false
class User < ActiveRecord::Base

Returns +self+ if the password is correct, otherwise +false+. 
def authenticate(unencrypted_password)
  BCrypt::Password.new(password_digest).is_password?(unencrypted_password) && self
end

def password=(unencrypted_password)

user.password_digest # => "$2a$10$4LEA7r4YmNHtvlAvHhsYAeZmk/xeUVtMTYqwIvYY76EW5GUqDiP4."
user.password = 'mUc3m00RsqyRe'
user.password_digest # => nil
user.password = nil
user = User.new

end
has_secure_password validations: false
class User < ActiveRecord::Base

new password is not empty.
Encrypts the password into the +password_digest+ attribute, only if the 
def password=(unencrypted_password)
  if unencrypted_password.nil?
    self.password_digest = nil
  elsif !unencrypted_password.empty?
    @password = unencrypted_password
    cost = ActiveModel::SecurePassword.min_cost ? BCrypt::Engine::MIN_COST : BCrypt::Engine.cost
    self.password_digest = BCrypt::Password.create(unencrypted_password, cost: cost)
  end
end

def password_confirmation=(unencrypted_password) 

def password_confirmation=(unencrypted_password)
  @password_confirmation = unencrypted_password
end