http: allow custom User-Agent for outgoing HTTP requests

internal/backend/httpuseragent_roundtripper.go

@@ -0,0 +1,25 @@
+package backend
+
+import "net/http"
+
+// httpUserAgentRoundTripper is a custom http.RoundTripper that modifies the User-Agent header
+// of outgoing HTTP requests.
+type httpUserAgentRoundTripper struct {
+	userAgent string
+	rt        http.RoundTripper
+}
+
+func newCustomUserAgentRoundTripper(rt http.RoundTripper, userAgent string) *httpUserAgentRoundTripper {
+	return &httpUserAgentRoundTripper{
+		rt:        rt,
+		userAgent: userAgent,
+	}
+}
+
+// RoundTrip modifies the User-Agent header of the request and then delegates the request
+// to the underlying RoundTripper.
+func (c *httpUserAgentRoundTripper) RoundTrip(req *http.Request) (*http.Response, error) {
+	req = req.Clone(req.Context())
+	req.Header.Set("User-Agent", c.userAgent)
+	return c.rt.RoundTrip(req)
+}