Filters the HTML output for the protected post password form.
Description
If modifying the password field, please note that the WordPress database schema limits the password field to 255 characters regardless of the value of the minlength or maxlength attributes or other validation that may be added to the input.
Parameters
$outputstring- The password form HTML output.
$postWP_Post- Post object.
$invalid_passwordstring- The invalid password message.
Source
return apply_filters( 'the_password_form', $output, $post, $invalid_password );
This is a working example and 9999 is the priority and you can adjust accordingly.