fix(input.prometheus): Read bearer token from file every time (#14191)

plugins/inputs/prometheus/kubernetes.go

@@ -8,6 +8,7 @@ import (
 	"net"
 	"net/http"
 	"net/url"
+	"os"
 	"os/user"
 	"path/filepath"
 	"strconv"
@@ -92,7 +93,16 @@ func (p *Prometheus) startK8s(ctx context.Context) error {
 				return
 			case <-time.After(time.Second):
 				if p.isNodeScrapeScope {
-					err = p.cAdvisor(ctx, config.BearerToken)
+					bearerToken := config.BearerToken
+					if config.BearerTokenFile != "" {
+						bearerTokenBytes, err := os.ReadFile(config.BearerTokenFile)
+						if err != nil {
+							p.Log.Errorf("Error reading bearer token file hence falling back to BearerToken: %s", err.Error())
+						} else {
+							bearerToken = string(bearerTokenBytes)
+						}
+					}
+					err = p.cAdvisor(ctx, bearerToken)
 					if err != nil {
 						p.Log.Errorf("Unable to monitor pods with node scrape scope: %s", err.Error())
 					}