mvn deploy to Exchange fails with 401 Unauthorized or "Artifact could not be resolved" - Connected App credential format in settings.xml

PROBLEM

Publishing to Anypoint Exchange via Maven fails with: Exchange publication failed: Artifact could not be resolved or a 401 Unauthorized from the Exchange Maven repository.

ROOT CAUSE

Anypoint Exchange's Maven facade (v3) does not support direct Anypoint Platform username/password authentication when Multi-Factor Authentication (MFA) is enforced on the organization. The Maven client has no mechanism to complete an interactive MFA challenge during a build, so credentials are rejected at the authentication layer before any artifact resolution occurs.

The supported authentication pattern is a Connected App (Client Credentials grant). However, the credentials must be passed in the exact format the Exchange v3 Maven facade expects.