From 70b93ea693d565f0911968a81a853b48dfbd7fe4 Mon Sep 17 00:00:00 2001
From: Dhia Ayachi <dhia@hashicorp.com>
Date: Fri, 13 May 2022 14:05:22 -0400
Subject: [PATCH] When a host header is defined override `req.Host` in the
 metrics ui (#13071)

* When a host header is defined override the req.Host in the metrics ui endpoint.

* add changelog
---
 .changelog/13071.txt | 3 +++
 agent/ui_endpoint.go | 6 +++++-
 2 files changed, 8 insertions(+), 1 deletion(-)
 create mode 100644 .changelog/13071.txt

diff --git a/.changelog/13071.txt b/.changelog/13071.txt
new file mode 100644
index 000000000..2493e5875
--- /dev/null
+++ b/.changelog/13071.txt
@@ -0,0 +1,3 @@
+```release-note:bug
+Fix a bug when configuring an `add_headers` directive named `Host` the header is not set for `v1/internal/ui/metrics-proxy/` endpoint.
+```
diff --git a/agent/ui_endpoint.go b/agent/ui_endpoint.go
index c9fb82d08..1a8d5591a 100644
--- a/agent/ui_endpoint.go
+++ b/agent/ui_endpoint.go
@@ -740,7 +740,11 @@ func (s *HTTPHandlers) UIMetricsProxy(resp http.ResponseWriter, req *http.Reques
 
 	// Add any configured headers
 	for _, h := range cfg.AddHeaders {
-		req.Header.Set(h.Name, h.Value)
+		if strings.ToLower(h.Name) == "host" {
+			req.Host = h.Value
+		} else {
+			req.Header.Set(h.Name, h.Value)
+		}
 	}
 
 	log.Debug("proxying request", "to", u.String())