feat: complete remaining Go backend modules

backend/internal/httpapi/auth_compat.go

@@ -0,0 +1,41 @@
+package httpapi
+
+import (
+	"net/http"
+	"net/url"
+)
+
+// NewAuthCompatibilityHandler preserves the legacy external-login endpoints
+// after platform password login became the only supported authentication flow.
+func NewAuthCompatibilityHandler() http.Handler { return authCompatibilityHandler{} }
+
+type authCompatibilityHandler struct{}
+
+func (authCompatibilityHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
+	if r.URL.Path != "/api/auth/login" && r.URL.Path != "/api/auth/callback" && r.URL.Path != "/api/auth/captcha" {
+		http.NotFound(w, r)
+		return
+	}
+	if r.Method != http.MethodGet {
+		w.Header().Set("Allow", http.MethodGet)
+		w.WriteHeader(http.StatusMethodNotAllowed)
+		return
+	}
+	if r.URL.Path == "/api/auth/captcha" {
+		writeJSON(w, http.StatusOK, map[string]any{"enabled": false, "message": "平台账号登录不使用外部验证码。"})
+		return
+	}
+	location := "/auth/login"
+	if r.URL.Path == "/api/auth/callback" {
+		location += "?error=callback_failed"
+	}
+	if base, err := url.Parse(absoluteRequestURL(r)); err == nil && base.IsAbs() {
+		base.Path, base.RawPath, base.RawQuery, base.Fragment = "/auth/login", "", "", ""
+		if r.URL.Path == "/api/auth/callback" {
+			base.RawQuery = "error=callback_failed"
+		}
+		location = base.String()
+	}
+	w.Header().Set("Location", location)
+	w.WriteHeader(http.StatusTemporaryRedirect)
+}