fix(turnstile): route CAPTCHA verification through the configured proxy (#38412) (#38420)

Backport #38412

Fixes #38217

Co-authored-by: Lovepreet Singh <lovepreet.singh61182@gmail.com>
Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

modules/util/sync.go

@@ -0,0 +1,51 @@
+// Copyright 2026 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package util
+
+import (
+	"sync"
+	"sync/atomic"
+)
+
+type onceValueResult[T any] struct {
+	value T
+	panic any
+}
+
+// OnceValue is similar to Golang's "sync.OnceValue", but can be reset.
+type OnceValue[T any] struct {
+	Func func() T
+	mu   sync.Mutex
+	res  atomic.Pointer[onceValueResult[T]]
+}
+
+func (o *OnceValue[T]) Value() T {
+	res := o.res.Load()
+	if res == nil {
+		o.mu.Lock()
+		defer o.mu.Unlock()
+		res = o.res.Load()
+		if res == nil {
+			res = &onceValueResult[T]{}
+			defer func() {
+				res.panic = recover()
+				o.res.Store(res)
+				if res.panic != nil {
+					panic(res.panic)
+				}
+			}()
+			res.value = o.Func()
+		}
+	}
+	if res.panic != nil {
+		panic(res.panic)
+	}
+	return res.value
+}
+
+func (o *OnceValue[T]) Reset() {
+	o.mu.Lock()
+	defer o.mu.Unlock()
+	o.res.Store(nil)
+}

modules/util/sync_test.go

@@ -0,0 +1,49 @@
+// Copyright 2026 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package util
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestOnceValue(t *testing.T) {
+	t.Run("RepeatCall", func(t *testing.T) {
+		callCount := 0
+		o := OnceValue[int]{Func: func() int {
+			callCount++
+			return 42
+		}}
+		assert.Equal(t, 42, o.Value())
+		assert.Equal(t, 42, o.Value())
+		assert.Equal(t, 1, callCount)
+		o.Reset()
+		assert.Equal(t, 42, o.Value())
+		assert.Equal(t, 2, callCount)
+		assert.Equal(t, 42, o.Value())
+		assert.Equal(t, 2, callCount)
+	})
+
+	t.Run("Panic", func(t *testing.T) {
+		callCount := 0
+		doPanic := true
+		o := OnceValue[int]{Func: func() int {
+			callCount++
+			if doPanic {
+				panic("some error")
+			}
+			return 42
+		}}
+		assert.PanicsWithValue(t, "some error", func() { o.Value() })
+		assert.PanicsWithValue(t, "some error", func() { o.Value() })
+		assert.Equal(t, 1, callCount)
+		doPanic = false
+		o.Reset()
+		assert.Equal(t, 42, o.Value())
+		assert.Equal(t, 2, callCount)
+		assert.Equal(t, 42, o.Value())
+		assert.Equal(t, 2, callCount)
+	})
+}