投稿する際にログインユーザーの情報をDBに保存したい

前提・実現したいこと

お世話になります。
SpringSecurityでログインしているユーザー情報を投稿する際にDBに保存したいと考えております。
現在はuseridを直接formに入力して投稿しているので、入力せずにログイン情報を投稿に紐付けたいです。
SpringSecurityでのログイン認証は実装済みです。

該当のソースコード

Recruit

java
1package com.recruit.model;
2
3import javax.persistence.Entity;
4import javax.persistence.GeneratedValue;
5import javax.persistence.GenerationType;
6import javax.persistence.Id;
7import javax.persistence.JoinColumn;
8import javax.persistence.ManyToOne;
9
10import lombok.Getter;
11import lombok.Setter;
12
13@Getter
14@Setter
15@Entity
16public class Recruit {
17
18	@Id
19	@GeneratedValue(strategy = GenerationType.AUTO)
20	private Long id;
21
22	private String mashine;
23
24	private String reason;
25
26	private String friendId;
27
28	private String game;
29
30	@ManyToOne
31	@JoinColumn(name="user_id")
32	private SiteUser user;
33
34}

RecruitController

java
1package com.recruit.controller;
2
3import org.springframework.beans.factory.annotation.Autowired;
4import org.springframework.security.core.Authentication;
5import org.springframework.stereotype.Controller;
6import org.springframework.ui.Model;
7import org.springframework.validation.BindingResult;
8import org.springframework.validation.annotation.Validated;
9import org.springframework.web.bind.annotation.GetMapping;
10import org.springframework.web.bind.annotation.ModelAttribute;
11import org.springframework.web.bind.annotation.PathVariable;
12import org.springframework.web.bind.annotation.PostMapping;
13
14import com.recruit.model.Recruit;
15import com.recruit.repository.RecruitRepository;
16
17import lombok.RequiredArgsConstructor;
18
19@RequiredArgsConstructor
20@Controller
21public class RecruitController {
22	@Autowired
23	private final RecruitRepository recruitRepository;
24
25	@GetMapping("/index")
26	public  String index(Authentication loginUser,Model model) {
27		model.addAttribute("username",loginUser.getName());
28		model.addAttribute("recruits",recruitRepository.findAll());
29		return "index";
30	}
31
32	@GetMapping("/new")
33	public String addRecruit(@ModelAttribute Recruit recruit,Authentication loginUser,Model model) {
34		model.addAttribute("username",loginUser.getName());
35		return "form";
36	}
37
38	@PostMapping("/process")
39	public String process(@Validated @ModelAttribute Recruit recruit,BindingResult result, Authentication loginUser) {
40		if(result.hasErrors()) {
41			return "form";
42		}
43		recruitRepository.save(recruit);
44		return "redirect:/index";
45	}
46
47	@GetMapping("/edit/{id}")
48	public String editRecruit(@PathVariable Long id, Model model) {
49		model.addAttribute("recruit",recruitRepository.findById(id));
50		return "form";
51	}
52
53	@GetMapping("/delete/{id}")
54	public String deleteRecruit(@PathVariable Long id) {
55		recruitRepository.deleteById(id);
56		return "redirect:/index";
57	}
58}

form.html

HTML
1<!DOCTYPE html>
2<html xmlns:th="http://www.thymeleaf.org">
3<head>
4<meta charset="UTF-8">
5<th:block th:insert="fragments/base :: header"></th:block>
6</head>
7<body id="page-top">
8<th:block th:insert="fragments/header"></th:block>
9	<div id="wrapper">
10		<div id="content-wrapper" class="d-flex flex-column">
11			<div id="content">
12				<div class="container-fluid">
13					<!-- Data -->
14					<div class="card shadow my-4">
15						<div class="card-header py-3" >
16							<h6 class="m-0 font-weight-bold text-primary">募集投稿</h6>
17						</div>
18						<div class="card-body">
19							<div class="table-responsive">
20								<form th:action="@{/process}" th:object="${recruit}" method="post">
21									<input type="hidden" th:field="*{id}">
22									<div class="form-group">
23										<label for="name">機種</label>
24										<input type="text" class="form-control" th:errorclass="is-invalid" th:field="*{mashine}">
25										<div class="invalid-feedback" th:errors="*{mashine}"></div>
26									</div>
27									<div class="form-group">
28										<label for="name">募集内容</label>
29										<input type="text" class="form-control" th:errorclass="is-invalid" th:field="*{reason}">
30										<div class="invalid-feedback" th:errors="*{reason}"></div>
31									</div>
32									<div class="form-group">
33										<label for="name">フレンドコード</label>
34										<input type="text" class="form-control" th:errorclass="is-invalid" th:field="*{friendId}">
35										<div class="invalid-feedback" th:errors="*{friendId}"></div>
36									</div>
37									<div class="form-group">
38										<label for="name">ゲーム名</label>
39										<input type="text" class="form-control" th:errorclass="is-invalid" th:field="*{game}">
40										<div class="invalid-feedback" th:errors="*{game}"></div>
41									</div>
42<!-- ここを入力せずに保存できるようにしたい -->
43									<div class="form-group">
44										<label for="name">ユーザー名</label>
45										<input type="text" class="form-control" th:errorclass="is-invalid" th:field="*{user}">
46										<div class="invalid-feedback" th:errors="*{user}"></div>
47									</div>
48
49
50									<hr class="sidebar-divider my-4">
51
52									<button class="btn btn-primary btn-block col-md-4">
53										<i class="fas fa-edit fa-fw"></i>
54										<span class="text">投稿する</span>
55									</button>
56								</form>
57							</div>
58						</div>
59					</div>
60				</div>
61			</div>
62		</div>
63	</div>
64</body>
65</html>