outposts/proxy: show full error message when user is authenticated

Signed-off-by: Jens Langhammer <jens.langhammer@beryju.org>

internal/outpost/proxyv2/application/error.go

@@ -1,6 +1,7 @@
 package application
 
 import (
+	"fmt"
 	"html/template"
 	"net/http"
 
@@ -8,8 +9,9 @@ import (
 )
 
 // NewProxyErrorHandler creates a ProxyErrorHandler using the template given.
-func NewProxyErrorHandler(errorTemplate *template.Template) func(http.ResponseWriter, *http.Request, error) {
+func (a *Application) newProxyErrorHandler(errorTemplate *template.Template) func(http.ResponseWriter, *http.Request, error) {
 	return func(rw http.ResponseWriter, req *http.Request, proxyErr error) {
+		claims, _ := a.getClaims(req)
 		log.WithError(proxyErr).Warning("Error proxying to upstream server")
 		rw.WriteHeader(http.StatusBadGateway)
 		data := struct {
@@ -21,6 +23,9 @@ func NewProxyErrorHandler(errorTemplate *template.Template) func(http.ResponseWr
 			Message:     "Error proxying to upstream server",
 			ProxyPrefix: "/akprox",
 		}
+		if claims != nil {
+			data.Message = fmt.Sprintf("Error proxying to upstream server: %s", proxyErr.Error())
+		}
 		err := errorTemplate.Execute(rw, data)
 		if err != nil {
 			http.Error(rw, "Internal Server Error", http.StatusInternalServerError)

internal/outpost/proxyv2/application/mode_proxy.go

@@ -29,7 +29,7 @@ func (a *Application) configureProxy() error {
 	}
 	rp := &httputil.ReverseProxy{Director: a.proxyModifyRequest(u)}
 	rp.Transport = ak.NewTracingTransport(context.TODO(), a.getUpstreamTransport())
-	rp.ErrorHandler = NewProxyErrorHandler(templates.GetTemplates())
+	rp.ErrorHandler = a.newProxyErrorHandler(templates.GetTemplates())
 	rp.ModifyResponse = a.proxyModifyResponse
 	a.mux.PathPrefix("/").HandlerFunc(func(rw http.ResponseWriter, r *http.Request) {
 		claims, err := a.getClaims(r)