add debug logging for user backend registration
add debug logging for user backend registration

bluelml/core,bluelml/core,bluelml/core,nextcloud/server,Ardinis/server,sharidas/core,nextcloud/server,pollopolea/core,andreas-p/nextcloud-server,michaelletzgus/nextcloud-server,michaelletzgus/nextcloud-server,xx621998xx/server,pmattern/server,bluelml/core,sharidas/core,whitekiba/server,pmattern/server,jbicha/server,pixelipo/server,cernbox/core,michaelletzgus/nextcloud-server,cernbox/core,lrytz/core,pmattern/server,pollopolea/core,pollopolea/core,xx621998xx/server,xx621998xx/server,endsguy/server,pmattern/server,andreas-p/nextcloud-server,IljaN/core,pmattern/server,pixelipo/server,nextcloud/server,Ardinis/server,cernbox/core,sharidas/core,xx621998xx/server,endsguy/server,IljaN/core,jbicha/server,owncloud/core,andreas-p/nextcloud-server,lrytz/core,andreas-p/nextcloud-server,whitekiba/server,owncloud/core,jbicha/server,Ardinis/server,lrytz/core,jbicha/server,sharidas/core,owncloud/core,pixelipo/server,endsguy/server,xx621998xx/server,owncloud/core,IljaN/core,endsguy/server,phil-davis/core,cernbox/core,pollopolea/core,whitekiba/server,lrytz/core,pixelipo/server,endsguy/server,IljaN/core,lrytz/core,nextcloud/server,owncloud/core,whitekiba/server,bluelml/core,IljaN/core,sharidas/core,cernbox/core,michaelletzgus/nextcloud-server,pixelipo/server,jbicha/server,Ardinis/server,andreas-p/nextcloud-server,Ardinis/server,whitekiba/server,pollopolea/core