[clientCertAuth] Nil pointer dereference on HTTP response when http.Get() fails

[rustiqly]

Description

In gnmi_server/clientCertAuth.go around line 161, resp.StatusCode is accessed even when http.Get() returns (nil, err). The current code checks resp != nil for the defer but then unconditionally accesses resp.StatusCode in the error check.

Current code

resp, err := http.Get(url)
if resp != nil { defer resp.Body.Close() }
if err != nil || resp.StatusCode != http.StatusOK {  // resp may be nil here!

Fix

Check err != nil first, return early, then access resp:

resp, err := http.Get(url)
if err != nil {
    return err
}
defer resp.Body.Close()
if resp.StatusCode != http.StatusOK {

Impact

Panic in the gNMI server when client certificate authentication makes an HTTP call that fails at the network level.