mas-cli is the upstream binary that currently provides the CLI and server subcommand used by start.sh.
share/ will contain the frontend assets, manifest, policy wasm, translations, and templates that MAS expects.
mas-config.template.yaml is the Cloudron-aware configuration template that start.sh expands into /app/data/configs/mas.yaml at runtime.

During build time we will download the official matrix-authentication-service release (Docker or the prebuilt tarball) into this directory so that the package can start the MAS server as soon as the app boots.