Fix safari cookie session bug (go-gitea#24772)

Partically backport go-gitea#24330

Related: go-gitea#24176

Maybe fix go-gitea#24770

(cherry picked from commit 64cc691)

modules/context/context.go

@@ -473,13 +473,33 @@ func (ctx *Context) JSON(status int, content interface{}) {
 	}
 }
 
+func removeSessionCookieHeader(w http.ResponseWriter) {
+	cookies := w.Header()["Set-Cookie"]
+	w.Header().Del("Set-Cookie")
+	for _, cookie := range cookies {
+		if strings.HasPrefix(cookie, setting.SessionConfig.CookieName+"=") {
+			continue
+		}
+		w.Header().Add("Set-Cookie", cookie)
+	}
+}
+
 // Redirect redirects the request
 func (ctx *Context) Redirect(location string, status ...int) {
 	code := http.StatusSeeOther
 	if len(status) == 1 {
 		code = status[0]
 	}
 
+	if strings.Contains(location, "://") || strings.HasPrefix(location, "//") {
+		// Some browsers (Safari) have buggy behavior for Cookie + Cache + External Redirection, eg: /my-path => https://other/path
+		// 1. the first request to "/my-path" contains cookie
+		// 2. some time later, the request to "/my-path" doesn't contain cookie (caused by Prevent web tracking)
+		// 3. Gitea's Sessioner doesn't see the session cookie, so it generates a new session id, and returns it to browser
+		// 4. then the browser accepts the empty session, then the user is logged out
+		// So in this case, we should remove the session cookie from the response header
+		removeSessionCookieHeader(ctx.Resp)
+	}
 	http.Redirect(ctx.Resp, ctx.Req, location, code)
 }
 

modules/context/context_test.go

@@ -0,0 +1,24 @@
+// Copyright 2023 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package context
+
+import (
+	"net/http"
+	"net/http/httptest"
+	"testing"
+
+	"code.gitea.io/gitea/modules/setting"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestRemoveSessionCookieHeader(t *testing.T) {
+	w := httptest.NewRecorder()
+	w.Header().Add("Set-Cookie", (&http.Cookie{Name: setting.SessionConfig.CookieName, Value: "foo"}).String())
+	w.Header().Add("Set-Cookie", (&http.Cookie{Name: "other", Value: "bar"}).String())
+	assert.Len(t, w.Header().Values("Set-Cookie"), 2)
+	removeSessionCookieHeader(w)
+	assert.Len(t, w.Header().Values("Set-Cookie"), 1)
+	assert.Contains(t, "other=bar", w.Header().Get("Set-Cookie"))
+}