HDFS external tables using account other than dbadmin

Customer gave us a username and password for an account to access HDFS. How do I set that in Vertica 9.3.x? They created a read-only account for us to test external tables. I looked into delegation but not sure that does it, or if it does, how to set up. If we need them to make changes we would need to submit a ticket with very specific step by step, so I'm hoping we can set this client side (well, in Vertica as a client of HDFS!) somehow.