Compile Time Constant Injection

We plug a few constants into code at compile-time. We do this to avoid hard-coding these values and hamper their public visibilty.

Constant	Bundle	System Property
OAuth client ID	login	oauth.client.id
OAuth client secret	login	oauth.client.secret
Google Analytics Tracking ID	usagetracking	ga.tracking.id

The Java classes that hold these constant values are auto-generated from template Java source files, using the templating-maven-plugin. The values are populated from system properties in the auto-gen process. That is, for example, mvn -Doauth.client.id=id1234 templating:filter-sources or mvn -Doauth.client.id=id1234 package will result in injecting id1234 as an OAuth client ID.