Add an environment variable to enable customizing the log target (#1243)

Signed-off-by: Christine Dodrill <xe@tailscale.com>

logpolicy/logpolicy.go

@@ -17,6 +17,7 @@ import (
 	"log"
 	"net"
 	"net/http"
+	"net/url"
 	"os"
 	"os/exec"
 	"path/filepath"
@@ -387,6 +388,13 @@ func New(collection string) *Policy {
 		HTTPC: &http.Client{Transport: newLogtailTransport(logtail.DefaultHost)},
 	}
 
+	if val, ok := os.LookupEnv("TAILSCALE_LOG_TARGET"); ok {
+		log.Println("You have enabled a non-default log target. Doing without being told to by Tailscale staff or your network administrator will make getting support difficult.")
+		c.BaseURL = val
+		u, _ := url.Parse(val)
+		c.HTTPC = &http.Client{Transport: newLogtailTransport(u.Host)}
+	}
+
 	filchBuf, filchErr := filch.New(filepath.Join(dir, cmdName), filch.Options{})
 	if filchBuf != nil {
 		c.Buffer = filchBuf