Log data Masking in AEM

Create an OSGi bundle and deploy. Are you new to writing OSGi bundles?  If so -- read:

https://helpx.adobe.com/experience-manager/using/first-osgi.html

Because the OSGi bundle is implemented as  Java - you can use Java to perform a Mask. Here is a Stackoverflow of how to mask in Java:

http://stackoverflow.com/questions/12148281/mask-string-with-characters

If you need to get/read AEM user data - then use Jackrabbit API in the service. 

Using Jackrabbit UserManager APIs to create AEM Users and Groups

Developing AEM OSGi bundles that use Jackrabbit UserManager APIs

I need to override the OOTB logger service in which i have to add my regex configuration where author can configure log file name. pattern matching for logging and other OOTB configuration. How can i override the default one so that my service should get picked.

"I need to override the OOTB logger service"

See these AEM doc topics for information:

https://docs.adobe.com/docs/en/cq/5-6-1/deploying/configure_logging.html

http://docs.adobe.com/docs/en/cq/5-6-1/deploying/monitoring_and_maintaining.html#Create a Custom Log File

See:

Name: org.apache.sling.commons.log.names
Type: String[] (String + Multi)
Value: specify the OSGi services for which the Logger is to log messages; for example, all of the following:

• org.apache.sling
• org.apache.felix
• com.day

You can write a log service - that is where you need to inject Java app logic to meet your mask requirements.