Step by step config JDBC Realm using MVNForum Database
1. Go to [MVNFORUM_HOME]\contrib\jdbcRealm\build.properties change some path 
    commons-logging.jar = [MYVIETNAM_HOME]/lib/commons-logging-1.1.jar
    driver.jar = [MVNFORUM_HOME]/driver/mysql-connector-java-3.0.17-ga-bin.jar
    catalina.home=[CATALINA_HOME]

2. Edit this realm for database connection in file when neccessary
    [MVNFORUM_HOME]\contrib\jdbcRealm\conf\mvn-jdbc-realm.xml

3. Run 
    [MVNFORUM_HOME]\contrib\jdbcRealm>ant deploy-all

4. Replace Realm in [CATALINA_HOME]\conf\server.xml with a sample realm in file config/realm-server.xml

    replace 
    <Realm className="org.apache.catalina.realm.UserDatabaseRealm"
                 debug="0" resourceName="UserDatabase"/>
    with
    <Realm className="com.mvnsoft.auth.realm.MVNTomcatJDBCRealm"
                 debug="0" resourceName="UserDatabase"/>

5. Enable single-sign-on in tomcat: go to file [CATALINA_HOME]\conf\server.xml uncomment this line:

    <Valve className="org.apache.catalina.authenticator.SingleSignOn"
                   debug="0"/>

6. Start Tomcat

7. Test with link: 
http://<server_name>:<port>/sample-realm/realm/index.jsp or 
http://<server_name>:<port>/sample-realm/realm/login.jsp

NOTES:
[CATALINA_HOME] is where Tomcat is installed
[MVNFORUM_HOME] is where mvnforum is.
By default, mvnforum has a only account: admin/admin.
You can log in with this account

8. After that you come to mvnforum's index page, you will see that user admin has already login into mvnforum.
