Authenticating users with usermeta fields

Ok seems like you have a few moving parts here…

1. You want to add a new meta field (unique code) to the user meta for all users

2. You want to modify the default login form by adding an extra field… a unique code field

3. This unique code field should allow the user to login if they have provided the same unique code in the login form

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1. I’m going to assume you’ve added this meta, if not, I suggest using carbon-fields to achieve this

   Container::make( 'user_meta', 'Login Meta' )
   ->add_fields( array(
       Field::make( 'text', 'unique_code', 'Unique Code' ),
   ));
   

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2. To hook into the login form you’ll want to make use of the login_form action

   add_action( 'login_form', function(){
     echo '<input type="text" name="unique_code" placeholder="Enter your unique code here" />';
   });
   

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3. Authenticating with this unique code field

you’ll then want to look at the authenticate filter which you can hook into to force authenticate the user based on this posted “unique_code” field

 add_filter( 'authenticate', function( $user, $username, $password ){

      //do the check for the unique_code field here, 
      //which should be available in the $_POST object


     return $user;
  });

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hope this helps, cheers