Authors and Categories

function pippin_taxonomy_add_new_meta_field() {
    // this will add the custom meta field to the add new term page
    ?>
    <div class="form-field">
        <label for="term_meta[custom_term_meta]"><?php _e( 'Select Users to Include', 'pippin' ); ?></label>
        <?php $authors = get_users();
              foreach($authors as $author) { ?>
              <input style="width:auto;" type="checkbox" name="term_meta[<?php echo $author->ID; ?>]" id="term_meta" value="<?php echo $author->ID; ?>">
              <?php echo $author->user_nicename; ?><br />
            <?php } ?>
    </div>
<?php
}
add_action( 'category_add_form_fields', 'pippin_taxonomy_add_new_meta_field', 10, 2 );

function pippin_taxonomy_edit_meta_field($term) {

    // put the term ID into a variable
    $t_id = $term->term_id;

    // retrieve the existing value(s) for this meta field. This returns an array
    $term_meta = get_option( "taxonomy_$t_id" ); ?>

    <tr class="form-field">
    <th scope="row" valign="top"><label for="term_meta[custom_term_meta]"><?php _e( 'Select Users to Include', 'pippin' ); ?></label></th>
        <td>
            <?php $authors = get_users();
              foreach($authors as $author) {
                $user_id = $author->ID;
               if(in_array($user_id, $term_meta)) { ?>
               <input type="hidden" name="term_meta[<?php echo $author->ID; ?>]" value="">
              <input style="width:auto;" type="checkbox" name="term_meta[<?php echo $author->ID; ?>]" id="term_meta" value="<?php echo $author->ID; ?>" checked="checked">
              <?php echo $author->user_nicename; ?><br />
            <?php } else { ?>
            <input style="width:auto;" type="checkbox" name="term_meta[<?php echo $author->ID; ?>]" id="term_meta" value="<?php echo $author->ID; ?>">
              <?php echo $author->user_nicename; ?><br />
            <?php }
            } ?>
        </td>
    </tr>
<?php
}
add_action( 'category_edit_form_fields', 'pippin_taxonomy_edit_meta_field', 10, 2 );

function save_taxonomy_custom_meta( $term_id ) {
        $t_id = $term_id;
        $term_meta = get_option( "taxonomy_$t_id" );
        $cat_keys = array_keys( $_POST['term_meta'] );
        foreach ( $cat_keys as $key ) {
            if ( isset ( $_POST['term_meta'][$key] ) ) {
                $term_meta[$key] = $_POST['term_meta'][$key];
            }
        // Save the option array.
        update_option( "taxonomy_$t_id", $term_meta );
    }
}
add_action( 'edited_category', 'save_taxonomy_custom_meta', 10, 2 );
add_action( 'create_category', 'save_taxonomy_custom_meta', 10, 2 );