* guix/svn-download.scm (<svn-reference>): Add fields for optional credentials. (svn-fetch): Pass credentials to build-side "svn-fetch". * guix/build/svn.scm (svn-fetch): Pass optional credentials to svn command.
* guix/svn-download.scm, guix/build/svn.scm: New files. * Makefile.am (MODULES): Add them. Signed-off-by: Ludovic Courtès <ludo@gnu.org>