Be more permissive of Content-Encoding responses.  If unrecognized, do not throw an HttpException.  There is some discussion about why some servers (for whatever reason) return something unexpected (e.g. 'none') at http://www.pimcore.org/board/viewtopic.php?f=5&t=460 e.g. https://ralingenmusikklag.no/ returns a Content-Encoding: none.  The specification reading is that it SHOULD return one of the known values.  But that is different from MUST return one.

The upshot is you get an entity back.   And the receiving application code can figure out how it treats it.

The workaround is to override/reimplement a HttpResponseInterceptor