Add logback configuration for contacts sample.

samples/contacts/src/main/webapp/WEB-INF/classes/logback.xml

@@ -0,0 +1,14 @@
+<configuration>
+  <appender name="STDOUT" class="ch.qos.logback.core.ConsoleAppender">
+    <encoder>
+      <pattern>%d{HH:mm:ss.SSS} [%thread] %-5level %logger{36} - %msg%n</pattern>
+    </encoder>
+  </appender>
+
+  <logger name="org.springframework.security" level="DEBUG"/>
+
+  <root level="INFO">
+    <appender-ref ref="STDOUT" />
+  </root>
+
+</configuration>