On the symfony blog today, there's a new post that looks at creating a conditional validator in the context of a classic login form for the framework.

Jon works on a symfony 1.1 project with a classic login form. The form is composed of two fields: a username and a password. The validation rules are quite straightforward: he wants each field to be required and he wants to check the correctness of the password.

They show how to set up a normal login widget and how to apply a sfValidatorCallback in the configure() method to check the values in the form. This method checks the username and password values and tosses an error with sfValidatorError if a problem is found.