I’ve added the SRTM 90m DEM to a new bucket for now while we find a better home for it.
In you SNAP installation you can edit the snap.auxdata.properties file with
DEM.srtm3GeoTiffDEM_HTTP = http://skywatch-auxdata.s3-us-west-2.amazonaws.com/dem/SRTM90/tiff/
The next update will have a proper source set by default