Merge properties files with Maven assembly

I have a problem with maven assembly plugin.

I have a maven project which use several jars. Each jar contains configuration files. With another project, I use maven assembly plugin to assemble all configurations in unique jar.

All work fine but unfortunately, two files are the same name and the second overwrites the first.

I don't achieve to tell maven to merge the two files instead of overwrite.

Someone knows how to do that ?

Thanks.