notification-sentinel: lower-case x-ms-date header for correct HMAC (#4288)

Author: ebirn

cmd/notification-sentinel/main.go

@@ -40,7 +40,8 @@ var logger hclog.Logger = hclog.New(&hclog.LoggerOptions{
 })
 
 func (s *SentinelPlugin) getAuthorizationHeader(now string, length int, name string) (string, error) {
-	xHeaders := "X-Ms-Date:" + now
+	// Azure calculates HMAC with this header in lower-case
+	xHeaders := "x-ms-date:" + now
 
 	cfg := s.PluginConfigByName[name]
 
@@ -94,7 +95,9 @@ func (s *SentinelPlugin) Notify(ctx context.Context, notification *protobufs.Not
 	req.Header.Set("Content-Type", "application/json")
 	req.Header.Set("Log-Type", cfg.LogType)
 	req.Header.Set("Authorization", authorization)
-	req.Header.Set("X-Ms-Date", now)
+	// to match lower-case header in HMAC calculation it must not be auto-Canonicalized
+	// https://pkg.go.dev/net/http#Header.Set
+	req.Header["x-ms-date"] = []string{now}
 
 	client := &http.Client{}