Come on guys, why didn't anyone who already resolved this issue post the solution?
Okay, here it goes:
svn ls http://svn.example.com/repository
It will ask for your credentials:
Authentication realm: http://svn.example.com:80 Repository Name
Password for 'user':
NOW HERE IS THE TRICK:
ATTENTION! Your password for authentication realm:
http://svn.example.com:80 Repository Name
can only be stored to disk unencrypted! You are advised to configure
your system so that Subversion can store passwords encrypted, if
possible. See the documentation for details.
You can avoid future appearances of this warning by setting the value
of the 'store-plaintext-passwords' option to either 'yes' or 'no' in
Store password unencrypted (yes/no)?
and that's it, bye bye Error 500!