feat(oidcgate): synthetic success handler mirrors X-* headers to response

cmd/oidcgate/success.go

@@ -0,0 +1,43 @@
+package main
+
+import (
+	"net/http"
+	"strings"
+)
+
+// mirrorAllowedHeaders is the set of NON-X-prefixed request headers that the
+// success handler copies onto the response. The traefikoidc middleware sets
+// "Authorization: Bearer ..." via the templated-header feature when operators
+// configure it, and proxies need that to flow upstream.
+var mirrorAllowedHeaders = map[string]struct{}{
+	"Authorization": {},
+}
+
+// successHandler is the http.Handler installed as the middleware's `next`.
+// When the middleware reaches this handler the request is authenticated; we
+// mirror the X-* (and a small allow-list of non-X-*) headers the middleware
+// stamped onto req.Header back onto the response so upstream proxies can
+// capture them via auth_request_set / authResponseHeaders / copy_headers,
+// then write 200 with an empty body.
+func newSuccessHandler() http.Handler {
+	return http.HandlerFunc(func(rw http.ResponseWriter, req *http.Request) {
+		for name, values := range req.Header {
+			if !shouldMirror(name) {
+				continue
+			}
+			for _, v := range values {
+				rw.Header().Add(name, v)
+			}
+		}
+		rw.WriteHeader(http.StatusOK)
+	})
+}
+
+func shouldMirror(name string) bool {
+	if strings.HasPrefix(name, "X-") || strings.HasPrefix(name, "x-") {
+		return true
+	}
+	canonical := http.CanonicalHeaderKey(name)
+	_, ok := mirrorAllowedHeaders[canonical]
+	return ok
+}

cmd/oidcgate/success_test.go

@@ -0,0 +1,57 @@
+package main
+
+import (
+	"net/http"
+	"net/http/httptest"
+	"strings"
+	"testing"
+)
+
+func TestSuccessHandler_Writes200(t *testing.T) {
+	h := newSuccessHandler()
+	rec := httptest.NewRecorder()
+	req := httptest.NewRequest(http.MethodGet, "/x", nil)
+	h.ServeHTTP(rec, req)
+	if rec.Code != http.StatusOK {
+		t.Fatalf("status: want 200, got %d", rec.Code)
+	}
+}
+
+func TestSuccessHandler_MirrorsForwardedHeaders(t *testing.T) {
+	h := newSuccessHandler()
+	rec := httptest.NewRecorder()
+	req := httptest.NewRequest(http.MethodGet, "/x", nil)
+	req.Header.Set("X-Forwarded-User", "[email protected]")
+	req.Header.Set("X-Forwarded-Email", "[email protected]")
+	req.Header.Set("X-Custom-Templated", "value")
+	req.Header.Set("Authorization", "Bearer token-from-template")
+	req.Header.Set("Cookie", "session=should-NOT-mirror")
+
+	h.ServeHTTP(rec, req)
+
+	if got := rec.Header().Get("X-Forwarded-User"); got != "[email protected]" {
+		t.Errorf("X-Forwarded-User: want mirrored, got %q", got)
+	}
+	if got := rec.Header().Get("X-Forwarded-Email"); got != "[email protected]" {
+		t.Errorf("X-Forwarded-Email: want mirrored, got %q", got)
+	}
+	if got := rec.Header().Get("X-Custom-Templated"); got != "value" {
+		t.Errorf("X-Custom-Templated: want mirrored (X- prefix), got %q", got)
+	}
+	if got := rec.Header().Get("Authorization"); got != "Bearer token-from-template" {
+		t.Errorf("Authorization: want mirrored (templated bearer), got %q", got)
+	}
+	if got := rec.Header().Get("Cookie"); got != "" {
+		t.Errorf("Cookie must NOT be mirrored, got %q", got)
+	}
+}
+
+func TestSuccessHandler_EmptyBody(t *testing.T) {
+	h := newSuccessHandler()
+	rec := httptest.NewRecorder()
+	req := httptest.NewRequest(http.MethodGet, "/x", nil)
+	h.ServeHTTP(rec, req)
+	if body := strings.TrimSpace(rec.Body.String()); body != "" {
+		t.Fatalf("body: want empty, got %q", body)
+	}
+}