OAuth 登录记住发起页：回调后回到登录前所在的前台 origin（开发时 3000/8080 分离不再落错站）

backend/internal/api/comments.go

@@ -10,6 +10,7 @@ import (
 	"encoding/hex"
 	"errors"
 	"net/http"
+	"net/url"
 	"strconv"
 	"strings"
 	"time"
@@ -24,6 +25,7 @@ import (
 const (
 	readerCookie   = "one_reader"
 	oauthStateCook = "one_oauth_state"
+	oauthBackCook  = "one_oauth_back"
 	maxCommentLen  = 500
 	editWindow     = 10 * time.Minute
 )
@@ -72,6 +74,8 @@ func (a *API) authLogout(w http.ResponseWriter, r *http.Request) {
 
 // githubLogin 跳转 GitHub 授权页。state 防 CSRF 存短命 cookie；
 // 授权完成回到 callback 后必须带上同一个值。
+// 同时把发起登录的前台 origin 记下来（one_oauth_back），
+// callback 用它跳回去——开发时前端 3000 / 后端 8080 分离才不会落错站。
 func (a *API) githubLogin(w http.ResponseWriter, r *http.Request) {
 	if !a.GH.Enabled() {
 		httpx.NotFound(w)
@@ -80,6 +84,12 @@ func (a *API) githubLogin(w http.ResponseWriter, r *http.Request) {
 	state := randHex(16)
 	http.SetCookie(w, &http.Cookie{Name: oauthStateCook, Value: state, Path: "/",
 		HttpOnly: true, MaxAge: 600})
+	if ref := r.Referer(); ref != "" {
+		if u, err := url.Parse(ref); err == nil && u.Scheme != "" && u.Host != "" {
+			http.SetCookie(w, &http.Cookie{Name: oauthBackCook,
+				Value: u.Scheme + "://" + u.Host, Path: "/", HttpOnly: true, MaxAge: 600})
+		}
+	}
 	http.Redirect(w, r, a.GH.LoginURL(a.Cfg.SiteURL+"/api/auth/callback/github", state), http.StatusFound)
 }
 
@@ -120,7 +130,15 @@ func (a *API) githubCallback(w http.ResponseWriter, r *http.Request) {
 	token, _ := a.ReaderSessions.Issue(reader.ID)
 	http.SetCookie(w, &http.Cookie{Name: auth.ReaderCookie, Value: token, Path: "/",
 		HttpOnly: true, SameSite: http.SameSiteLaxMode, MaxAge: int((30 * 24 * time.Hour).Seconds())})
-	http.Redirect(w, r, "/", http.StatusFound)
+	// 回到发起登录的前台；没有记录（直接敲 URL 进来的）就回站点根
+	back := a.Cfg.SiteURL
+	if ck, err := r.Cookie(oauthBackCook); err == nil && ck.Value != "" {
+		if u, err := url.Parse(ck.Value); err == nil && (u.Scheme == "http" || u.Scheme == "https") && u.Host != "" && u.Path == "" {
+			back = u.Scheme + "://" + u.Host
+		}
+	}
+	http.SetCookie(w, &http.Cookie{Name: oauthBackCook, Value: "", Path: "/", MaxAge: -1})
+	http.Redirect(w, r, back, http.StatusFound)
 }
 
 func randHex(n int) string {