Revert "Only allow some specific headers (#11)" (#14)

This reverts commit ce4390d.

proxy/handlers.go

@@ -12,6 +12,9 @@ import (
 )
 
 type APIReverseProxy struct {
+	upstreamURL *url.URL
+	host        string
+
 	reverseProxy *httputil.ReverseProxy
 }
 
@@ -24,25 +27,6 @@ func NewAPIReverseProxy(upstream string, host string) (*APIReverseProxy, error)
 	reverseProxy := &httputil.ReverseProxy{
 		Director: func(req *http.Request) {
 			rewriteRequestURL(req, upstreamURL)
-			headers := http.Header{}
-
-			allowedHeaders := []string{
-				"X-Forwarded-For",
-				"X-Forwarded-Host",
-				"X-Forwarded-Proto",
-				"User-Agent",
-			}
-			for _, header := range allowedHeaders {
-				vals, ok := req.Header[header]
-				if !ok {
-					continue
-				}
-
-				for _, val := range vals {
-					headers.Add(header, val)
-				}
-			}
-			req.Header = headers
 			req.Host = host
 		},
 		ModifyResponse: func(resp *http.Response) error {
@@ -54,6 +38,8 @@ func NewAPIReverseProxy(upstream string, host string) (*APIReverseProxy, error)
 	}
 
 	return &APIReverseProxy{
+		upstreamURL:  upstreamURL,
+		host:         host,
 		reverseProxy: reverseProxy,
 	}, nil
 }