Afternoon Wayne, had to wait until I had time to hunt down links for you.
To reiterate: I am unsure GeoMesa can include GeoServer user interface contributions in the code hosted at LocationTech. To implement a GeoServer user interface contribution reference must be made to GPL classes making up the GeoServer API.
I skipped a bit quickly past this common problem, in order to focus on the solution the GeoServer community has come up with. GeoServer is well aware that not all data source can meet the restrictions of the GPL license. As a result:
1) All data access code has been moved in the GeoTools project, where appropriate interfaces are provided with a less restrictive "business friendly" LGPL license is used.
2) Connection details required for data access is "advertised" as meta-data by an implementor as part of the DataStoreFactorySPI interface getParams() method. Using this metadata GeoServer will generate a user interface suitable for casual use.
3) Finally (if the generated user interface is not considered usable enough) we have a section of the code base called "community" (informal - no QA or docs) or "extensions" (formal - QA and Doc requirements met) where the few user interface classes that must be GPL can be hosted.
Armed with this background let me provide a couple of examples.
DB2
DB2 minimal example where auto-generated user interface is enough:
In this case DB2 supported has been added by implementing a JDBCDialect and supporting classes from the GeoTools project.
ArcSDE
ArcSDE example uses this LGPL/GPL separation to allow interaction with a proprietary API.
The implementation of ArcSDECoverageStoreEditPanel implements the GPL interface StoredEditPanel. This is packaged as a GeoServer extension in order to hold code using GPL interfaces. The ArcSDEDataStore is extends the ContentStore base class from the GeoTools project.
I hope those two examples are sufficient? The use of GeoTools LGPL Interfaces allows implementors a great deal of freedom in choice of license (BSD, EPL, MIT, LGPL or even GPL).
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Jody