JAVA-23896 Clarify "Guide to @ConfigurationProperties in Spring Boot" article (#14642)

spring-boot-modules/spring-boot-properties/src/main/java/com/baeldung/configurationproperties/ImmutableCredentials.java

@@ -1,6 +1,7 @@
 package com.baeldung.configurationproperties;
 
 import org.springframework.boot.context.properties.ConfigurationProperties;
+import org.springframework.boot.context.properties.bind.ConstructorBinding;
 
 @ConfigurationProperties(prefix = "mail.credentials")
 public class ImmutableCredentials {
@@ -9,12 +10,19 @@ public class ImmutableCredentials {
     private final String username;
     private final String password;
 
+    @ConstructorBinding
     public ImmutableCredentials(String authMethod, String username, String password) {
         this.authMethod = authMethod;
         this.username = username;
         this.password = password;
     }
 
+    public ImmutableCredentials(String username, String password) {
+        this.username = username;
+        this.password = password;
+        this.authMethod = "Default";
+    }
+
     public String getAuthMethod() {
         return authMethod;
     }