SecureDrop copies Onion Service credentials to Monitor Server

SecureDrop is an open-source whistleblower submission system that media organizations can use to securely accept documents from, and communicate with anonymous sources. From 2.13.0 until 2.16.1, running the securedrop-admin install Ansible playbook with journalist alerts disabled leaves the journalist alert key filename empty, causing the copy task to transfer every file in ~/.config/securedrop-admin/, including Onion Service client authentication credentials, to the Monitor Server. An attacker must first compromise the privileged Monitor Server to obtain the credentials, and the credentials remain an additional protection layer rather than sufficient access by themselves because the Journalist Interface still requires a username, passphrase, and MFA, while SSH access still requires SSH keys. This issue is fixed in version 2.16.1.