Missing authentication for local web interface in Arc before v1.6.0

When configuring Arc (e.g. during the first setup), a local web interface is provided to ease the configuration process. Such web interface lacks authentication and may thus be abused by a local attacker or malware running on the machine itself. A malicious local user or process, during a window of opportunity when the local web interface is active, may be able to extract sensitive information or change Arc's configuration. This could also lead to arbitrary code execution if a malicious update package is installed.