custom-profile-fields.php

<?php
/**
 * Render the extra profile fields on the backend
 */
function extra_user_profile_fields( $user ) { ?>
    <h3><?php _e("Extra profile information", "blank"); ?></h3>

    <table class="form-table">
	    <tr>
	        <th><label for="external_username"><?php _e("External Username"); ?></label></th>
	        <td>
	            <input type="text" name="external_username" id="external_username" value="<?php echo esc_attr( get_the_author_meta( 'external_username', $user->ID ) ); ?>" class="regular-text" /><br />
	        </td>
	    </tr>
	    <tr>
	    <th><label for="external_password"><?php _e("External Password"); ?></label></th>
	        <td>
	            <input type="text" name="external_password" id="external_password" value="<?php echo esc_attr( get_the_author_meta( 'external_password', $user->ID ) ); ?>" class="regular-text" /><br />
	        </td>
	    </tr>
    </table>
<?php }
add_action( 'show_user_profile', 'extra_user_profile_fields' );
add_action( 'edit_user_profile', 'extra_user_profile_fields' );

/**
 * Save custom profile field values
 */
function save_extra_user_profile_fields( $user_id ) {

    if ( !current_user_can( 'edit_user', $user_id ) ) { 
        return false; 
    }

    update_user_meta( $user_id, 'external_username', $_POST['external_username'] );
	update_user_meta( $user_id, 'external_password', $_POST['external_password'] );

}
add_action( 'personal_options_update', 'save_extra_user_profile_fields' );
add_action( 'edit_user_profile_update', 'save_extra_user_profile_fields' );

/**
 * Shortcode to render these fields on a specific page
 */
function private_profile_fields_shortcode( $atts ){
	ob_start();
	if( is_user_logged_in() ){ 
		$user_id = get_current_user_id();

		?>
		<table class="form-table">
		    <tr>
		        <th><label for="external_username"><?php _e("External Username"); ?></label></th>
		        <td>
		            <?php echo esc_attr( get_the_author_meta( 'external_username', $user_id ) ); ?>
		        </td>
		    </tr>
		    <tr>
		    <th><label for="external_password"><?php _e("External Password"); ?></label></th>
		        <td>
		            <?php echo esc_attr( get_the_author_meta( 'external_password', $user_id ) ); ?>
		        </td>
		    </tr>
	    </table>
		<?php
	}
	$temp_content = ob_get_contents();
	ob_end_clean();
	return $temp_content;
}
add_shortcode( 'private_profile_fields', 'private_profile_fields_shortcode' );