cmd/relui: fix website upload username

Unlike the coordinator, the website doesn't want the user- prefix on the
username.

For golang/go#51797.

Change-Id: I169bdf1dd8ffd7cad6fccb2cf752be4271efe094
Reviewed-on: https://go-review.googlesource.com/c/build/+/411063
Reviewed-by: Dmitri Shuralyov <dmitshur@golang.org>
Auto-Submit: Heschi Kreinick <heschi@google.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
Run-TryBot: Heschi Kreinick <heschi@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
diff --git a/cmd/relui/main.go b/cmd/relui/main.go
index d25f13d..67e9f0f 100644
--- a/cmd/relui/main.go
+++ b/cmd/relui/main.go
@@ -19,6 +19,7 @@
 	"math/rand"
 	"net/http"
 	"net/url"
+	"strings"
 	"time"
 
 	"cloud.google.com/go/storage"
@@ -182,7 +183,7 @@
 	if err != nil {
 		return fmt.Errorf("invalid website upload URL %q: %v", *websiteUploadURL, err)
 	}
-	u.Query().Set("user", auth.Username)
+	u.Query().Set("user", strings.TrimPrefix("user-", auth.Username))
 	u.Query().Set("key", auth.Password)
 	resp, err := http.Post(u.String(), "application/json", bytes.NewReader(req))
 	if err != nil {