feat(invite): add GET /v1/invites/{code} + rework POST accept as signup+join

- V027 migration: add invited_by FK column on household_invite
- HouseholdInvite entity: add invitedBy field, set on createInvite
- New DTOs: InviteInfoResponse, AcceptInviteRequest
- HouseholdService: add getInviteInfo(), rewrite acceptInvite(code, name, email, password) — creates UserAccount + joins household in one transaction
- HouseholdController: GET /v1/invites/{code} (unauthenticated), POST /v1/invites/{code}/accept creates session after join
- SecurityConfig: permitAll() for /v1/invites/*, sessionFixation().changeSessionId()

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/src/main/java/com/recipeapp/auth/SecurityConfig.java

@@ -24,11 +24,13 @@ public class SecurityConfig {
                 .authorizeHttpRequests(auth -> auth
                         .requestMatchers("/v1/auth/signup", "/v1/auth/login").permitAll()
                         .requestMatchers("/swagger-ui/**", "/v3/api-docs/**").permitAll()
+                        .requestMatchers("/v1/invites/*").permitAll()
                         .requestMatchers("/v1/admin/**").hasAuthority("ROLE_ADMIN")
                         .anyRequest().authenticated())
                 .exceptionHandling(ex -> ex
                         .authenticationEntryPoint(new HttpStatusEntryPoint(HttpStatus.UNAUTHORIZED)))
                 .sessionManagement(session -> session
+                        .sessionFixation().changeSessionId()
                         .maximumSessions(1));
 
         return http.build();

backend/src/main/java/com/recipeapp/household/HouseholdController.java

@@ -1,10 +1,17 @@
 package com.recipeapp.household;
 
+import com.recipeapp.auth.entity.UserAccount;
 import com.recipeapp.common.ApiResponse;
 import com.recipeapp.household.dto.*;
+import jakarta.servlet.http.HttpServletRequest;
 import jakarta.validation.Valid;
 import org.springframework.http.HttpStatus;
 import org.springframework.http.ResponseEntity;
+import org.springframework.security.authentication.UsernamePasswordAuthenticationToken;
+import org.springframework.security.core.authority.SimpleGrantedAuthority;
+import org.springframework.security.core.context.SecurityContext;
+import org.springframework.security.core.context.SecurityContextHolder;
+import org.springframework.security.web.context.HttpSessionSecurityContextRepository;
 import org.springframework.web.bind.annotation.*;
 
 import java.security.Principal;
@@ -71,11 +78,34 @@ public class HouseholdController {
         return ResponseEntity.ok(ApiResponse.success(response));
     }
 
-    @PostMapping("/invites/{code}/accept")
-    public ResponseEntity<ApiResponse<AcceptInviteResponse>> acceptInvite(
-            Principal principal,
-            @PathVariable String code) {
-        AcceptInviteResponse response = householdService.acceptInvite(principal.getName(), code);
+    @GetMapping("/invites/{code}")
+    public ResponseEntity<ApiResponse<InviteInfoResponse>> getInviteInfo(@PathVariable String code) {
+        InviteInfoResponse response = householdService.getInviteInfo(code);
         return ResponseEntity.ok(ApiResponse.success(response));
     }
+
+    @PostMapping("/invites/{code}/accept")
+    public ResponseEntity<ApiResponse<AcceptInviteResponse>> acceptInvite(
+            @PathVariable String code,
+            @Valid @RequestBody AcceptInviteRequest request,
+            HttpServletRequest httpRequest) {
+        AcceptInviteResponse response = householdService.acceptInvite(
+                code, request.name(), request.email(), request.password());
+        authenticateInSession(request.email(), httpRequest);
+        return ResponseEntity.ok(ApiResponse.success(response));
+    }
+
+    private void authenticateInSession(String email, HttpServletRequest request) {
+        var oldSession = request.getSession(false);
+        if (oldSession != null) {
+            oldSession.invalidate();
+        }
+        var auth = UsernamePasswordAuthenticationToken.authenticated(
+                email, null, List.of(new SimpleGrantedAuthority("ROLE_USER")));
+        SecurityContext context = SecurityContextHolder.createEmptyContext();
+        context.setAuthentication(auth);
+        SecurityContextHolder.setContext(context);
+        request.getSession(true).setAttribute(
+                HttpSessionSecurityContextRepository.SPRING_SECURITY_CONTEXT_KEY, context);
+    }
 }

backend/src/main/java/com/recipeapp/household/HouseholdService.java

@@ -6,6 +6,7 @@ import com.recipeapp.common.ConflictException;
 import com.recipeapp.common.ResourceNotFoundException;
 import com.recipeapp.common.ValidationException;
 import com.recipeapp.household.dto.*;
+import org.springframework.security.crypto.password.PasswordEncoder;
 import com.recipeapp.household.entity.Household;
 import com.recipeapp.household.entity.HouseholdInvite;
 import com.recipeapp.household.entity.HouseholdMember;
@@ -38,6 +39,7 @@ public class HouseholdService {
     private final IngredientCategoryRepository ingredientCategoryRepository;
     private final TagRepository tagRepository;
     private final VarietyScoreConfigRepository varietyScoreConfigRepository;
+    private final PasswordEncoder passwordEncoder;
 
     @Value("${app.base-url}")
     private String baseUrl;
@@ -52,7 +54,8 @@ public class HouseholdService {
                                  IngredientRepository ingredientRepository,
                                  IngredientCategoryRepository ingredientCategoryRepository,
                                  TagRepository tagRepository,
-                                 VarietyScoreConfigRepository varietyScoreConfigRepository) {
+                                 VarietyScoreConfigRepository varietyScoreConfigRepository,
+                                 PasswordEncoder passwordEncoder) {
         this.userAccountRepository = userAccountRepository;
         this.householdRepository = householdRepository;
         this.householdMemberRepository = householdMemberRepository;
@@ -61,6 +64,7 @@ public class HouseholdService {
         this.ingredientCategoryRepository = ingredientCategoryRepository;
         this.tagRepository = tagRepository;
         this.varietyScoreConfigRepository = varietyScoreConfigRepository;
+        this.passwordEncoder = passwordEncoder;
     }
 
     @Transactional
@@ -167,30 +171,45 @@ public class HouseholdService {
         String code = generateInviteCode();
         Instant expiresAt = Instant.now().plusSeconds(48 * 3600);
 
-        HouseholdInvite invite = householdInviteRepository.save(
-                new HouseholdInvite(household, code, expiresAt));
+        HouseholdInvite invite = new HouseholdInvite(household, code, expiresAt);
+        invite.setInvitedBy(member.getUser());
+        householdInviteRepository.save(invite);
 
         return toInviteResponse(invite);
     }
 
-    @Transactional
-    public AcceptInviteResponse acceptInvite(String userEmail, String code) {
-        UserAccount user = findUser(userEmail);
+    @Transactional(readOnly = true)
+    public InviteInfoResponse getInviteInfo(String code) {
+        HouseholdInvite invite = householdInviteRepository.findByInviteCode(code)
+                .orElseThrow(() -> new ResourceNotFoundException("Invite not found or invalid"));
 
-        if (householdMemberRepository.findByUserEmailIgnoreCase(userEmail).isPresent()) {
-            throw new ConflictException("User is already in a household");
+        if ("used".equals(invite.getStatus()) || invite.getExpiresAt().isBefore(Instant.now())) {
+            throw new ResourceNotFoundException("Invite not found or invalid");
+        }
+
+        String inviterName = invite.getInvitedBy() != null
+                ? invite.getInvitedBy().getDisplayName()
+                : invite.getHousehold().getCreatedBy().getDisplayName();
+
+        return new InviteInfoResponse(invite.getHousehold().getName(), inviterName);
+    }
+
+    @Transactional
+    public AcceptInviteResponse acceptInvite(String code, String name, String email, String rawPassword) {
+        if (userAccountRepository.existsByEmailIgnoreCase(email)) {
+            throw new ConflictException("Email already registered");
         }
 
         HouseholdInvite invite = householdInviteRepository.findByInviteCode(code)
-                .orElseThrow(() -> new ResourceNotFoundException("Invite not found"));
+                .orElseThrow(() -> new ResourceNotFoundException("Invite not found or invalid"));
 
-        if ("used".equals(invite.getStatus())) {
-            throw new ConflictException("Invite code already used");
-        }
-        if (invite.getExpiresAt().isBefore(Instant.now())) {
-            throw new ValidationException("Invite code has expired");
+        if ("used".equals(invite.getStatus()) || invite.getExpiresAt().isBefore(Instant.now())) {
+            throw new ResourceNotFoundException("Invite not found or invalid");
         }
 
+        UserAccount user = userAccountRepository.save(
+                new UserAccount(email, name, passwordEncoder.encode(rawPassword)));
+
         invite.setStatus("used");
         householdInviteRepository.save(invite);
 

backend/src/main/java/com/recipeapp/household/dto/AcceptInviteRequest.java

@@ -0,0 +1,11 @@
+package com.recipeapp.household.dto;
+
+import jakarta.validation.constraints.Email;
+import jakarta.validation.constraints.NotBlank;
+import jakarta.validation.constraints.Size;
+
+public record AcceptInviteRequest(
+        @NotBlank String name,
+        @NotBlank @Email String email,
+        @NotBlank @Size(min = 8) String password
+) {}

backend/src/main/java/com/recipeapp/household/dto/InviteInfoResponse.java

@@ -0,0 +1,6 @@
+package com.recipeapp.household.dto;
+
+public record InviteInfoResponse(
+        String householdName,
+        String inviterName
+) {}

backend/src/main/java/com/recipeapp/household/entity/HouseholdInvite.java

@@ -1,5 +1,6 @@
 package com.recipeapp.household.entity;
 
+import com.recipeapp.auth.entity.UserAccount;
 import jakarta.persistence.*;
 import java.time.Instant;
 import java.util.UUID;
@@ -16,6 +17,10 @@ public class HouseholdInvite {
     @JoinColumn(name = "household_id", nullable = false)
     private Household household;
 
+    @ManyToOne(fetch = FetchType.LAZY)
+    @JoinColumn(name = "invited_by")
+    private UserAccount invitedBy;
+
     @Column(name = "invite_code", nullable = false, unique = true, length = 20)
     private String inviteCode;
 
@@ -38,6 +43,8 @@ public class HouseholdInvite {
 
     public UUID getId() { return id; }
     public Household getHousehold() { return household; }
+    public UserAccount getInvitedBy() { return invitedBy; }
+    public void setInvitedBy(UserAccount invitedBy) { this.invitedBy = invitedBy; }
     public String getInviteCode() { return inviteCode; }
     public String getStatus() { return status; }
     public void setStatus(String status) { this.status = status; }