feat: terminal as a chosen OS user, create users from the panel (0.0.2)

- agent reports the OS user it runs as (enroll + poll header)
- per-machine terminal user on the edit page; defaults to the agent's own user (root on Linux)
- create a new user from the panel: name, password, optional sudo group
- show the reason in the terminal when a shell fails to start
- bump version to 0.0.2

internal/server/handlers_panel.go

@@ -1,9 +1,13 @@
 package server
 
 import (
+	"encoding/json"
+	"errors"
 	"fmt"
 	"log"
 	"net/http"
+	"net/url"
+	"slices"
 	"strconv"
 	"strings"
 	"time"
@@ -152,13 +156,135 @@ func (s *Server) handleAgentEdit(w http.ResponseWriter, r *http.Request) {
 		http.NotFound(w, r)
 		return
 	}
-	s.render(w, "edit.html", map[string]any{
+	data := map[string]any{
 		"Agent":         a,
 		"CSRF":          csrfToken(r),
 		"ServerVersion": Version,
 		"Outdated":      a.Version != "" && a.Version != Version,
 		"Updated":       r.URL.Query().Get("updated") == "1",
+		"UserOK":        r.URL.Query().Get("uok"),
+		"UserErr":       r.URL.Query().Get("uerr"),
+	}
+	// The user list lives on the machine, so it is only known while it is online.
+	if a.Online() {
+		if users, err := s.agentUsers(id); err == nil {
+			data["Users"] = users
+		} else {
+			data["UsersErr"] = err.Error()
+		}
+	}
+	s.render(w, "edit.html", data)
+}
+
+// usersTaskTimeout bounds how long the edit page waits for the agent.
+const usersTaskTimeout = 8 * time.Second
+
+// agentUsers asks the agent who it runs as and which users it can log in as.
+func (s *Server) agentUsers(agentID string) (*proto.SysUsersResult, error) {
+	taskID, ch := s.hub.CreateTask(agentID, proto.TaskSysUsers, nil)
+	defer s.hub.DiscardTask(taskID)
+	select {
+	case res := <-ch:
+		if !res.OK {
+			// Agents older than 0.0.2 don't know this task.
+			return nil, errors.New("клиент не поддерживает выбор пользователя — обновите его")
+		}
+		var out proto.SysUsersResult
+		if err := json.Unmarshal(res.Data, &out); err != nil {
+			return nil, errors.New("некорректный ответ клиента")
+		}
+		return &out, nil
+	case <-time.After(usersTaskTimeout):
+		return nil, errors.New("таймаут ожидания клиента")
+	}
+}
+
+// editUserRedirect returns to the edit page with a result banner.
+func editUserRedirect(w http.ResponseWriter, r *http.Request, id, key, msg string) {
+	http.Redirect(w, r, "/agents/"+id+"/edit?"+key+"="+url.QueryEscape(msg), http.StatusSeeOther)
+}
+
+// handleAgentSetUser picks the OS user terminals on this machine run as.
+func (s *Server) handleAgentSetUser(w http.ResponseWriter, r *http.Request) {
+	if !checkCSRF(r) {
+		http.Error(w, "bad csrf", http.StatusForbidden)
+		return
+	}
+	id := r.PathValue("id")
+	a, err := s.db.GetAgent(id)
+	if err != nil || a == nil {
+		http.NotFound(w, r)
+		return
+	}
+	name := strings.TrimSpace(r.FormValue("user"))
+	if !a.Online() {
+		editUserRedirect(w, r, id, "uerr", "Машина офлайн — сменить пользователя нельзя.")
+		return
+	}
+	// Only accept a user the machine itself reports, so a typo (or an agent too
+	// old to honour the choice) can't silently leave the terminal as root.
+	users, err := s.agentUsers(id)
+	if err != nil {
+		editUserRedirect(w, r, id, "uerr", err.Error())
+		return
+	}
+	if !slices.Contains(users.Users, name) {
+		editUserRedirect(w, r, id, "uerr", "Пользователя "+name+" нет на машине.")
+		return
+	}
+	if name == users.Current {
+		name = "" // follow the agent's own user
+	}
+	if err := s.db.SetAgentLoginUser(id, name); err != nil {
+		editUserRedirect(w, r, id, "uerr", "Не удалось сохранить.")
+		return
+	}
+	if admin := s.currentAdmin(r); admin != nil {
+		s.db.Audit(admin.ID, id, "set_user:"+firstNonEmpty(name, users.Current))
+	}
+	editUserRedirect(w, r, id, "uok", "Терминал будет открываться от "+firstNonEmpty(name, users.Current)+".")
+}
+
+// handleAgentAddUser creates a new OS user on the machine and switches the
+// terminal to it.
+func (s *Server) handleAgentAddUser(w http.ResponseWriter, r *http.Request) {
+	if !checkCSRF(r) {
+		http.Error(w, "bad csrf", http.StatusForbidden)
+		return
+	}
+	id := r.PathValue("id")
+	a, err := s.db.GetAgent(id)
+	if err != nil || a == nil {
+		http.NotFound(w, r)
+		return
+	}
+	if !a.Online() {
+		editUserRedirect(w, r, id, "uerr", "Машина офлайн — создать пользователя нельзя.")
+		return
+	}
+	name := strings.TrimSpace(r.FormValue("name"))
+	args, _ := json.Marshal(proto.SysUserAddArgs{
+		Name:     name,
+		Password: r.FormValue("password"),
+		Sudo:     r.FormValue("sudo") == "1",
 	})
+	taskID, ch := s.hub.CreateTask(id, proto.TaskSysUserAdd, args)
+	defer s.hub.DiscardTask(taskID)
+	select {
+	case res := <-ch:
+		if !res.OK {
+			editUserRedirect(w, r, id, "uerr", "Не удалось создать пользователя: "+res.Error)
+			return
+		}
+	case <-time.After(30 * time.Second):
+		editUserRedirect(w, r, id, "uerr", "Таймаут ожидания клиента.")
+		return
+	}
+	_ = s.db.SetAgentLoginUser(id, name)
+	if admin := s.currentAdmin(r); admin != nil {
+		s.db.Audit(admin.ID, id, "create_user:"+name)
+	}
+	editUserRedirect(w, r, id, "uok", "Пользователь "+name+" создан и выбран для терминала.")
 }
 
 // handleAgentUpdate asks the agent to download the latest binary and restart.