Implement flag --query-frontend.slow-query-logs-user-header

cmd/thanos/query_frontend.go

@@ -161,6 +161,8 @@ func registerQueryFrontend(app *extkingpin.App) {
 
 	cmd.Flag("query-frontend.vertical-shards", "Number of shards to use when distributing shardable PromQL queries. For more details, you can refer to the Vertical query sharding proposal: https://thanos.io/tip/proposals-accepted/202205-vertical-query-sharding.md").IntVar(&cfg.NumShards)
 
+	cmd.Flag("query-frontend.slow-query-logs-user-header", "Set the value of the field remote_user in the slow query logs to the value of the given HTTP header. Falls back to reading the user from the basic auth header.").PlaceHolder("<http-header-name>").Default("").StringVar(&cfg.CortexHandlerConfig.SlowQueryLogsUserHeader)
+
 	reqLogConfig := extkingpin.RegisterRequestLoggingFlags(cmd)
 
 	cmd.Setup(func(g *run.Group, logger log.Logger, reg *prometheus.Registry, tracer opentracing.Tracer, _ <-chan struct{}, _ bool) error {

internal/cortex/frontend/transport/handler.go

@@ -43,9 +43,10 @@ var (
 
 // Config for a Handler.
 type HandlerConfig struct {
-	LogQueriesLongerThan time.Duration `yaml:"log_queries_longer_than"`
-	MaxBodySize          int64         `yaml:"max_body_size"`
-	QueryStatsEnabled    bool          `yaml:"query_stats_enabled"`
+	LogQueriesLongerThan    time.Duration `yaml:"log_queries_longer_than"`
+	MaxBodySize             int64         `yaml:"max_body_size"`
+	QueryStatsEnabled       bool          `yaml:"query_stats_enabled"`
+	SlowQueryLogsUserHeader string        `yaml:"slow_query_logs_user_header"`
 }
 
 // Handler accepts queries and forwards them to RoundTripper. It can log slow queries,
@@ -176,7 +177,13 @@ func (f *Handler) reportSlowQuery(r *http.Request, responseHeaders http.Header,
 		thanosTraceID = traceID
 	}
 
-	remoteUser, _, _ := r.BasicAuth()
+	var remoteUser string
+	// Prefer reading remote user from header. Fall back to the value of basic authentication.
+	if f.cfg.SlowQueryLogsUserHeader != "" {
+		remoteUser = r.Header.Get(f.cfg.SlowQueryLogsUserHeader)
+	} else {
+		remoteUser, _, _ = r.BasicAuth()
+	}
 
 	logMessage := append([]interface{}{
 		"msg", "slow query detected",