Require authentication for remote gNOI KillProcess calls

[ashutosh-agrawal]

Why I did it

KillProcess changes host service state, but the handler currently continues when the telemetry server has no client authentication configured. A remote TCP client can therefore stop or restart an allowed service without authenticating.

Local Unix-socket access is different: it is restricted through the socket’s filesystem permissions and should continue to work.

How I did it

• Reject TCP KillProcess requests when no client authentication method is configured.
• Keep the existing authentication and authorization checks for configured clients.
• Preserve the filesystem-protected Unix-socket path.
• Add focused tests for both the rejected remote path and the permitted Unix-socket path.

How to verify it

go test ./gnmi_server \
    -run 'TestKillProcess(RejectsUnauthenticatedWrite|AllowsUnixSocketPeer)$' \
    -count=1

git diff --check passes. The focused Go tests were not run locally because this host does not have the Go/build environment; repository CI will provide that result.

Which release branch to backport (provide reason below if selected)

No backport requested.

Tested branch

• master
• N/A

Test result

Focused regression tests were added. Repository CI is pending.

Description for the changelog

Require authentication for remote gNOI KillProcess requests.

Link to config_db schema for YANG module changes

N/A

A picture of a cute animal (not mandatory but encouraged)

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