Instance methods shouldnt be added until you actually call has_secure_password

activemodel/lib/active_model/secure_password.rb

@@ -37,9 +37,12 @@ module ActiveModel
 
         validates_confirmation_of :password
         validates_presence_of     :password_digest
+        
+        include InstanceMethodsOnActivation
       end
     end
 
+    module InstanceMethodsOnActivation
       # Returns self if the password is correct, otherwise false.
       def authenticate(unencrypted_password)
         if BCrypt::Password.new(password_digest) == unencrypted_password
@@ -56,3 +59,4 @@ module ActiveModel
       end
     end
   end
+end