add AppUserReference to allow storing simple copyed version of appUser

commons-auth-core/src/main/java/io/rocketbase/commons/model/AppUser.java

@@ -102,4 +102,20 @@ protected void checkKeyValue(String key, String value) {
         Assert.hasLength(value, "Value must not be empty");
         Assert.state(value.length() <= 4000, "Value is too long - at least 4000 chars");
     }
+
+    /**
+     * convert current instance to a simple reference copy
+     *
+     * @return fresh created reference based on this {@link AppUser}
+     */
+    public AppUserReference toReference() {
+        return AppUserReference.builder()
+                .id(getId())
+                .username(getUsername())
+                .firstName(getFirstName())
+                .lastName(getLastName())
+                .email(getEmail())
+                .avatar(getAvatar())
+                .build();
+    }
 }

commons-auth-core/src/main/java/io/rocketbase/commons/model/AppUserReference.java

@@ -0,0 +1,28 @@
+package io.rocketbase.commons.model;
+
+import lombok.*;
+
+import java.io.Serializable;
+
+/**
+ * simplified {@link AppUser} without keyValues pairs, password etc...<br>
+ * used to store a simple representation as a copy of {@link AppUser}
+ */
+@Getter
+@Builder
+@NoArgsConstructor
+@AllArgsConstructor
+public class AppUserReference implements Serializable {
+
+    private String id;
+
+    private String username;
+
+    private String firstName;
+
+    private String lastName;
+
+    private String email;
+
+    private String avatar;
+}