Issue 44f1f49 has implemented a regex check for a range of characters. Matching one of those characters, the puppet run returns the error that a non-ASCII character is in password which is why the svn repository cannot be cloned.
Removing this part of the logic from file lib/puppet/provider/vcsrepo/svn.rb, the svn repository is successfully cloned, despite the presence of one of those "illegal" characters -- in our specific case, the open curly brace ('{'). Thus, at least some of the characters deemed "illegal" by the present code are in fact not "illegal".