Update transport.go to allow usage of http proxies

CHANGELOG.md

@@ -5,6 +5,8 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
 ## Unreleased
+### Fixed
+- `irma.HTTPTransport` now honours the `HTTP_PROXY`, `HTTPS_PROXY` and `NO_PROXY` environment variables, so irmago can run where outgoing traffic must pass through a proxy; it was the only outbound transport in irmago that ignored them. Operators with a system-wide proxy can keep internal traffic (requestor callbacks, keyshare and revocation servers) off it with `NO_PROXY`; loopback addresses are never proxied ([#423](https://github.com/privacybydesign/irmago/issues/423))
 
 ## [1.3.0] - 2026-08-12
 ### Added

irma/transport.go

@@ -86,8 +86,11 @@ func NewHTTPTransport(serverURL string, forceHTTPS bool) *HTTPTransport {
 	}
 
 	// Create a transport that dials with a SIGPIPE handler (which is only active on iOS).
-	// The settings are inspired on the defaults of http.DefaultTransport.
+	// The settings are inspired on the defaults of http.DefaultTransport, including its
+	// Proxy: outbound requests honour the HTTP_PROXY, HTTPS_PROXY and NO_PROXY environment
+	// variables, as the rest of irmago already does through http.DefaultTransport.
 	innerTransport := &http.Transport{
+		Proxy:                 http.ProxyFromEnvironment,
 		TLSClientConfig:       tlsClientConfig,
 		ForceAttemptHTTP2:     true,
 		MaxIdleConns:          100,

irma/transport_test.go

@@ -4,6 +4,7 @@ import (
 	"encoding/json"
 	"net/http"
 	"net/http/httptest"
+	"net/url"
 	"testing"
 
 	"github.com/stretchr/testify/require"
@@ -146,3 +147,28 @@ func TestJsonRequest_RemoteErrorBodyIsPreserved(t *testing.T) {
 		})
 	}
 }
+
+// TestNewHTTPTransport_UsesEnvironmentProxy covers issue #423: HTTPTransport was the
+// only outbound transport in irmago that left http.Transport.Proxy unset, so it ignored
+// the HTTP_PROXY/HTTPS_PROXY environment variables that everything routed through
+// http.DefaultTransport already honours.
+//
+// The proxy function is inspected directly rather than exercised against a real proxy,
+// because net/http reads the environment once behind a sync.Once: a test setting
+// HTTP_PROXY would only take effect if it happened to run before any other code in the
+// process resolved a proxy.
+func TestNewHTTPTransport_UsesEnvironmentProxy(t *testing.T) {
+	inner, ok := NewHTTPTransport("https://example.com", true).client.HTTPClient.Transport.(*http.Transport)
+	require.True(t, ok)
+	require.NotNil(t, inner.Proxy, "outbound transport must honour HTTP_PROXY/HTTPS_PROXY")
+
+	// Loopback destinations are never proxied, whatever the environment says, so local
+	// servers (including the ones in these tests) keep being dialled directly.
+	for _, dest := range []string{"http://localhost:8080/foo", "http://127.0.0.1:8080/foo"} {
+		u, err := url.Parse(dest)
+		require.NoError(t, err)
+		proxy, err := inner.Proxy(&http.Request{URL: u})
+		require.NoError(t, err)
+		require.Nil(t, proxy, "loopback destination %s must not be proxied", dest)
+	}
+}