feat : 이메일 인증 구현

src/main/java/com/hallym/rehab/domain/user/controller/SmtpController.java

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+package com.hallym.rehab.domain.user.controller;
+
+import com.hallym.rehab.domain.user.dto.EmailDTO;
+import com.hallym.rehab.domain.user.service.SmtpGmailSenderImpl;
+import lombok.RequiredArgsConstructor;
+import org.springframework.http.ResponseEntity;
+import org.springframework.web.bind.annotation.*;
+
+@RestController
+@RequestMapping("/email")
+@RequiredArgsConstructor
+public class SmtpController {
+    private final SmtpGmailSenderImpl senderService;
+
+    @GetMapping("/send-code/{email}")
+    public ResponseEntity<String> sendEmail(@PathVariable String email) {
+        senderService.sendEmail(email);
+        return ResponseEntity.ok("Email sent");
+    }
+
+    @PostMapping(value = "/verify-code/{email}", consumes = "application/json")
+    public ResponseEntity<String> sendEmailAndCode(@PathVariable String email, @RequestBody EmailDTO dto) {
+        if (senderService.verifyAuthCode(email, dto.getAuthCode())) {
+            return ResponseEntity.ok("Email verified");
+        }
+        return ResponseEntity.badRequest().body("Email verification failed");
+    }
+}

src/main/java/com/hallym/rehab/domain/user/dto/EmailDTO.java

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+package com.hallym.rehab.domain.user.dto;
+
+import lombok.Data;
+
+@Data
+public class EmailDTO {
+    private String authCode;
+}

src/main/java/com/hallym/rehab/domain/user/service/SmtpGmailSenderImpl.java

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+package com.hallym.rehab.domain.user.service;
+
+import com.hallym.rehab.global.util.RedisUtil;
+import lombok.RequiredArgsConstructor;
+import org.springframework.beans.factory.annotation.Value;
+import org.springframework.mail.SimpleMailMessage;
+import org.springframework.mail.javamail.JavaMailSender;
+import org.springframework.stereotype.Service;
+
+import java.util.Random;
+
+@Service
+@RequiredArgsConstructor
+public class SmtpGmailSenderImpl implements SmtpGmailSenderService{
+    private final JavaMailSender emailSender;
+    private final RedisUtil redisUtil;
+    @Value("${spring.mail.username}")
+    private String from;
+
+    @Override
+    public void sendEmail(String toEmail) {
+        if(redisUtil.existData(toEmail)) {
+            redisUtil.deleteData(toEmail);
+        }
+
+        String cipher = createCipher();
+        redisUtil.setDataExpire(toEmail, cipher, 60 * 5L);
+
+        SimpleMailMessage message = new SimpleMailMessage();
+        message.setFrom(from);
+        message.setTo(toEmail);
+        message.setSubject("이메일 인증번호를 알려드립니다.");
+        message.setText("5분안에 입력해야 합니다. \n" + "인증번호 : " + cipher);
+
+        emailSender.send(message);
+    }
+
+    @Override
+    public Boolean verifyAuthCode(String email, String authCode) {
+        String authCodeFoundByEmail = redisUtil.getData(email);
+        if (authCodeFoundByEmail == null) {
+            return false;
+        }
+        return authCodeFoundByEmail.equals(authCode);
+    }
+
+    @Override
+    public String createCipher() {
+        int leftLimit = 48; // number '0'
+        int rightLimit = 122; // alphabet 'z'ß
+        int targetStringLength = 6;
+        Random random = new Random();
+
+        return random.ints(leftLimit, rightLimit + 1)
+                .filter(i -> (i <=57 || i >=65) && (i <= 90 || i>= 97))
+                .limit(targetStringLength)
+                .collect(StringBuilder::new, StringBuilder::appendCodePoint, StringBuilder::append)
+                .toString();
+    }
+}

src/main/java/com/hallym/rehab/domain/user/service/SmtpGmailSenderService.java

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+package com.hallym.rehab.domain.user.service;
+
+public interface SmtpGmailSenderService {
+    void sendEmail(String toEmail);
+    Boolean verifyAuthCode(String email, String authCode);
+    String createCipher();
+}