How to create a database link with an OS Authenticated user?

Unfortunately, there is no command in Oracle that will let you do something similar to the following:

CREATE DATABASE LINK db_link_name IDENTIFIED EXTERNALLY ....;

The reason that you cannot create a database link with OS authentication is that you will be accessing a remote database running on a different server that you have not authenticated to. However, that does not mean that a user local to your database cannot connect to the remote database with a database authenticated user (using a userid and password).