Initialize Spring Boot backend with JWT auth

src/main/java/com/openisle/service/EmailService.java

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+package com.openisle.service;
+
+import org.springframework.beans.factory.annotation.Value;
+import org.springframework.http.HttpEntity;
+import org.springframework.http.HttpHeaders;
+import org.springframework.http.HttpMethod;
+import org.springframework.http.MediaType;
+import org.springframework.stereotype.Service;
+import org.springframework.web.client.RestTemplate;
+
+import java.util.HashMap;
+import java.util.Map;
+
+@Service
+public class EmailService {
+
+    @Value("${resend.api.key}")
+    private String apiKey;
+
+    private final RestTemplate restTemplate = new RestTemplate();
+
+    public void sendEmail(String to, String subject, String text) {
+        String url = "https://api.resend.com/emails"; // hypothetical endpoint
+
+        HttpHeaders headers = new HttpHeaders();
+        headers.setContentType(MediaType.APPLICATION_JSON);
+        headers.set("Authorization", "Bearer " + apiKey);
+
+        Map<String, String> body = new HashMap<>();
+        body.put("to", to);
+        body.put("subject", subject);
+        body.put("text", text);
+        body.put("from", "demo@openisle.example");
+
+        HttpEntity<Map<String, String>> entity = new HttpEntity<>(body, headers);
+        restTemplate.exchange(url, HttpMethod.POST, entity, String.class);
+    }
+}

src/main/java/com/openisle/service/JwtService.java

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+package com.openisle.service;
+
+import io.jsonwebtoken.Claims;
+import io.jsonwebtoken.Jwts;
+import io.jsonwebtoken.SignatureAlgorithm;
+import io.jsonwebtoken.security.Keys;
+import org.springframework.beans.factory.annotation.Value;
+import org.springframework.stereotype.Service;
+
+import java.security.Key;
+import java.util.Date;
+
+@Service
+public class JwtService {
+
+    @Value("${app.jwt.secret}")
+    private String secret;
+
+    @Value("${app.jwt.expiration}")
+    private long expiration;
+
+    private Key getSigningKey() {
+        return Keys.hmacShaKeyFor(secret.getBytes());
+    }
+
+    public String generateToken(String subject) {
+        Date now = new Date();
+        Date expiryDate = new Date(now.getTime() + expiration);
+        return Jwts.builder()
+                .setSubject(subject)
+                .setIssuedAt(now)
+                .setExpiration(expiryDate)
+                .signWith(getSigningKey(), SignatureAlgorithm.HS256)
+                .compact();
+    }
+
+    public String validateAndGetSubject(String token) {
+        Claims claims = Jwts.parserBuilder()
+                .setSigningKey(getSigningKey())
+                .build()
+                .parseClaimsJws(token)
+                .getBody();
+        return claims.getSubject();
+    }
+}

src/main/java/com/openisle/service/UserService.java

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+package com.openisle.service;
+
+import com.openisle.model.User;
+import com.openisle.repository.UserRepository;
+import lombok.RequiredArgsConstructor;
+import org.springframework.security.crypto.bcrypt.BCryptPasswordEncoder;
+import org.springframework.security.crypto.password.PasswordEncoder;
+import org.springframework.stereotype.Service;
+
+import java.util.Optional;
+
+@Service
+@RequiredArgsConstructor
+public class UserService {
+    private final UserRepository userRepository;
+    private final PasswordEncoder passwordEncoder = new BCryptPasswordEncoder();
+
+    public User register(String username, String email, String password) {
+        if (userRepository.findByUsername(username).isPresent() || userRepository.findByEmail(email).isPresent()) {
+            throw new RuntimeException("User already exists");
+        }
+        User user = new User();
+        user.setUsername(username);
+        user.setEmail(email);
+        user.setPassword(passwordEncoder.encode(password));
+        return userRepository.save(user);
+    }
+
+    public Optional<User> authenticate(String username, String password) {
+        return userRepository.findByUsername(username)
+                .filter(user -> passwordEncoder.matches(password, user.getPassword()));
+    }
+}