@qglaude You underestimate SNAP 
If you have opened and displayed a geocoded (WGS84) raster you can select âadd layerâ in the mapping tools:

Add a service URL of a WMS, for example the OWS terrestris OpenStreetMap
http://ows.terrestris.de/osm-gray/service?

Select a layer in the following dialogue:

Click âNextâ and âFinishâ - there you have it:
