title: Symfony 4+ form validation done in a controller action?
body: <p>I understand how constraints are applied in Form types, etc.</p>
  
  <p>But in the case of implementing a password reset, I need to check for the existence of an email and error if it does not exist.</p>
  
  <p>How might one achieve that in Symfony 4+?</p>
  
  <p>This doesn't seem to solve my issue:</p>
  
  <p><a href="https://symfony.com/doc/current/validation/raw_values.html" rel="nofollow noreferrer">https://symfony.com/doc/current/validation/raw_values.html</a></p>