Modified conf/tomcat-users.xml before
<role rolename="manager-gui"/>
<user username="user" password="password" roles="manager-gui"/>
But still can't access the management page.
Solution:
The new conf/Catalina/localhost/manager.xml content is as follows:
<Context privileged="true" antiResourceLocking="false"
docBase="${catalina.home}/webapps/manager">
<Valve className="org.apache.catalina.valves.RemoteAddrValve" allow="^.*$" />
</Context>