chore: add prometheus timing to latency endpoint (#7742)

* chore: Prometheus timing to latency endpoint

coderd/latencycheck.go

@@ -2,8 +2,6 @@ package coderd
 
 import (
 	"net/http"
-	"net/url"
-	"strings"
 )
 
 // LatencyCheck is an endpoint for the web ui to measure latency with.
@@ -11,22 +9,17 @@ import (
 // only be set in dev modes.
 //
 //nolint:revive
-func LatencyCheck(allowAll bool, allowedOrigins ...*url.URL) http.HandlerFunc {
-	allowed := make([]string, 0, len(allowedOrigins))
-	for _, origin := range allowedOrigins {
-		// Allow the origin without a path
-		tmp := *origin
-		tmp.Path = ""
-		allowed = append(allowed, strings.TrimSuffix(origin.String(), "/"))
-	}
-	if allowAll {
-		allowed = append(allowed, "*")
-	}
-	origins := strings.Join(allowed, ",")
+func LatencyCheck() http.HandlerFunc {
 	return func(rw http.ResponseWriter, r *http.Request) {
 		// Allowing timing information to be shared. This allows the browser
 		// to exclude TLS handshake timing.
-		rw.Header().Set("Timing-Allow-Origin", origins)
+		rw.Header().Set("Timing-Allow-Origin", "*")
+		// Always allow all CORs on this route.
+		rw.Header().Set("Access-Control-Allow-Origin", "*")
+		rw.Header().Set("Access-Control-Allow-Headers", "*")
+		rw.Header().Set("Access-Control-Allow-Credentials", "false")
+		rw.Header().Set("Access-Control-Allow-Methods", "*")
 		rw.WriteHeader(http.StatusOK)
+		_, _ = rw.Write([]byte("OK"))
 	}
 }