I can't override the user_pass hook because I use a websevcice to manage my users, I need to override the user_pass() to send a new password via my webservices.
This is what i did:

/**
* Implements hook_validate()
*/
function beneficiaire_user_pass_validate($form, &amp;$form_state){
    die('poc');
}

/**
* Implements hook_submit()
*/
function beneficiaire_user_pass_submit($form, &amp;$form_state){
    module_load_include('inc', 'beneficiaire', 'ws');
    global $user;

    if(beneficiaire_reset_password($user-&gt;name)){
        drupal_goto('login');
    }
}


My module is named beneficiaire.
I've cleaned my caches many times
when I enter a username in the form, it returns me 


  Sorry, %name is not recognized as a user name or an e-mail address


instead of 


  poc


An idea ?

Thank you
The main error is that, since your module's short name is beneficiaire, those are the implementations of hook_user_pass_validate() and hook_user_pass_submit(), which aren't hook Drupal utilizes. If you rename the functions beneficiaire_validate() and beneficiaire_submit(), those would not be hooks which are used as validation and submission handlers for the password change form.
See @Clive's answer for how adding form validation and submission handlers, keeping in mind that the validation handler is added with $form['#validate'][] = 'beneficiaire_user_pass_validate';.

As side notes:


If you want to check a validation handler is called, use form_set_error("", "beneficiaire_user_pass_validate() called");
To redirect the user after submitting a form, set $form_state['redirect'] as in $form_state['redirect'] = 'login';