User authentication\authorization upper-lower case

[Claudio Corona]

 Hi all. I have a problem with SVN. I have the (only) user 'test_user' (in
the 'passwd' file) having 'rw' on the entire repository. Why am I able to
get *authenticated* with the user  'TESTUSER' (but not *authorized* to
commit)? Note that only authenticated user can access and read from my
repository, so 'TESTUSER' should not be authenticated, as it happens for all
the users not appearing in the passwd file, for example the 'BlaBlaBla'
user.
Thanks