What is a recommended option for an integration approach from a security perspective?

Universal Containers requires Salesforce to send expense data to an accounting system. Each user has their own username/password credential to access the account system via integration.

What is a recommended option for an integration approach from a security perspective?
A . Set up a Named-Principal Named Credential and have the administrator set up the username/password.
B . Set up a Per-User Named Credential and have the users each set up their username/password.
C . Fire outbound messages to a middleware that stores the credentials instead of an Apex callout.
D . Use hierarchical custom settings to store the username/password allowing the Apex callout to read it.

Answer: B