Wordpress module to add and display a guest author's name and title

guest_author_with_title.php

<?php
/**
*
* Add ability to add guest authors
*/

function myblog_guest_author_name( $original_name ) {
  if (in_the_loop()) {
    $guest_name = get_post_meta( get_the_ID(), 'guest_author_name', true );
    return ( $guest_name ) ? $guest_name : $original_name;
  } else {
    return $original_name;
  }

}
add_filter( 'the_author', 'myblog_guest_author_name' );
add_filter( 'get_the_author_display_name', 'myblog_guest_author_name' );


function myblog_guest_author_meta_box( $post_type, $post ) {
  $screens = array( 'post', 'page' );
  foreach ( $screens as $screen ) {
    add_meta_box( 
      'guest_author_meta_box',
      __( 'myblog Guest Author','myblog' ),
      'myblog_render_guest_author_meta_box',
      $screen,
      'normal',
      'default'
    );
  }
}
add_action( 'add_meta_boxes', 'myblog_guest_author_meta_box', 10, 2 );

/**
 * Prints the box content.
 * 
 * @param WP_Post $post The object for the current post/page.
 */
function myblog_render_guest_author_meta_box( $post ) {

  // Add an nonce field so we can check for it later.
  wp_nonce_field( 'myblog_guest_author_meta_box', 'myblog_guest_author_meta_box_nonce' );

  /*
   * Use get_post_meta() to retrieve an existing value
   * from the database and use the value for the form.
   */
  $name_value = get_post_meta( $post->ID, 'guest_author_name', true );
  echo '<label for="guest_author_name">';
  _e( 'Name', 'myblog' );
  echo '</label> ';
  echo '<input type="text" id="guest_author_name" name="guest_author_name" value="' . esc_attr( $name_value ) . '" size="25" />';
  echo "<br>";
  $title_value = get_post_meta( $post->ID, 'guest_author_title', true );
  echo '<label for="guest_author_title">';
  _e( 'Title', 'myblog' );
  echo '</label> ';
  echo '<input type="text" id="guest_author_title" name="guest_author_title" value="' . esc_attr( $title_value ) . '" size="25" />';
}

/**
 * When the post is saved, saves our custom data.
 *
 * @param int $post_id The ID of the post being saved.
 */
function myblog_save_guest_author_meta_box( $post_id ) {

  /*
   * We need to verify this came from our screen and with proper authorization,
   * because the save_post action can be triggered at other times.
   */

  // Check if our nonce is set.
  if ( ! isset( $_POST['myblog_guest_author_meta_box_nonce'] ) ) {
    return;
  }

  // Verify that the nonce is valid.
  if ( ! wp_verify_nonce( $_POST['myblog_guest_author_meta_box_nonce'], 'myblog_guest_author_meta_box' ) ) {
    return;
  }

  // If this is an autosave, our form has not been submitted, so we don't want to do anything.
  if ( defined( 'DOING_AUTOSAVE' ) && DOING_AUTOSAVE ) {
    return;
  }

  // Check the user's permissions.
  if ( isset( $_POST['post_type'] ) && 'page' == $_POST['post_type'] ) {

    if ( ! current_user_can( 'edit_page', $post_id ) ) {
      return;
    }

  } else {

    if ( ! current_user_can( 'edit_post', $post_id ) ) {
      return;
    }
  }

  /* OK, it's safe for us to save the data now. */
  
  // Make sure that it is set and update the meta field in the database.
  if ( isset($_POST['guest_author_name'])) {
    update_post_meta( $post_id, 'guest_author_name', sanitize_text_field($_POST['guest_author_name']) );
  }
  if (isset($_POST['guest_author_title'])) {
    update_post_meta( $post_id, 'guest_author_title', sanitize_text_field($_POST['guest_author_title']) );
  } 
}
add_action( 'save_post', 'myblog_save_guest_author_meta_box' );


/**
 * Prints HTML with meta information for the current post author.
 */
function myblog_posted_by() {
  global $post;
  echo '<div class="author-info">';

  // Don't link up guest author names
  if (get_post_meta( $post->ID, 'guest_author_name', true ) != '') {
    $name_html =  esc_html( get_the_author() );
  } else {
    $name_html = '<a class="url fn n" href="' . esc_url( get_author_posts_url( get_the_author_meta( 'ID' ) ) ) . '">' . esc_html( get_the_author() ) . '</a>';
  }
  $byline = sprintf(
    _x( 'by %s', 'post author', 'myblog' ),
    '<span class="author vcard">' . $name_html . '</span>'
  );

  // Display gravatar
  echo get_avatar( get_the_author_meta( 'ID' ) , 34 );
  echo '<div class="meta">';
  echo '<span class="byline"> ' . $byline . '</span>';

  // Display (job) title 
  $guest_title = get_post_meta( $post->ID, 'guest_author_title', true );
  $title = ($guest_title != '') ? $guest_title : get_the_author_meta( "job-title" );

  echo '<span class="jobtitle">' . $title .'</span>';
  echo "</div>";
  echo "</div>";
}