feat: add authentication and tenant context

backend/src/main/java/com/linhelp/common/security/TenantContext.java

@@ -0,0 +1,44 @@
+package com.linhelp.common.security;
+
+public final class TenantContext {
+    private static final ThreadLocal<Scope> SCOPE = new ThreadLocal<Scope>();
+
+    private TenantContext() {
+    }
+
+    public static void set(Long tenantId, Long communityId) {
+        SCOPE.set(new Scope(tenantId, communityId));
+    }
+
+    public static Long tenantId() {
+        Scope scope = SCOPE.get();
+        return scope == null ? null : scope.tenantId();
+    }
+
+    public static Long communityId() {
+        Scope scope = SCOPE.get();
+        return scope == null ? null : scope.communityId();
+    }
+
+    public static void clear() {
+        SCOPE.remove();
+    }
+
+    private static class Scope {
+        private final Long tenantId;
+        private final Long communityId;
+
+        private Scope(Long tenantId, Long communityId) {
+            this.tenantId = tenantId;
+            this.communityId = communityId;
+        }
+
+        private Long tenantId() {
+            return tenantId;
+        }
+
+        private Long communityId() {
+            return communityId;
+        }
+    }
+}