fix(op): initialize http Headers in response objects (#637)

* fix(op): initialize http Headers in response objects

* fix test

---------

Co-authored-by: Livio Spring <livio.a@gmail.com>

pkg/op/error_test.go

@@ -428,7 +428,8 @@ func TestTryErrorRedirect(t *testing.T) {
 				parent: oidc.ErrInteractionRequired().WithDescription("sign in"),
 			},
 			want: &Redirect{
-				URL: "http://example.com/callback?error=interaction_required&error_description=sign+in&state=state1",
+				Header: make(http.Header),
+				URL:    "http://example.com/callback?error=interaction_required&error_description=sign+in&state=state1",
 			},
 			wantLog: `{
 						"level":"WARN",

pkg/op/server.go

@@ -218,7 +218,8 @@ type Response struct {
 // without custom headers.
 func NewResponse(data any) *Response {
 	return &Response{
-		Data: data,
+		Header: make(http.Header),
+		Data:   data,
 	}
 }
 
@@ -242,7 +243,10 @@ type Redirect struct {
 }
 
 func NewRedirect(url string) *Redirect {
-	return &Redirect{URL: url}
+	return &Redirect{
+		Header: make(http.Header),
+		URL:    url,
+	}
 }
 
 func (red *Redirect) writeOut(w http.ResponseWriter, r *http.Request) {