Configuration of the Alfresco Share application is done in a file called share-config-custom.xml. This file is typically located in /alfresco/web-extension/share-config-custom.xml somehere in the classpath. Usually /shared/classes/alfresco/web-extension.
However, if you are developing a module, it is nicer if you can distribute share-config-custom.xml with the amp or jar and also make sure it does not conflict with another module.
The way to achive this is to put it in the META-INF directory of your module jar.
The reason why this works is found in the slingshot-application-context.xml file