When accessing subversion repositories the error:

svn: E120190:  Error running context: An error occurred during authentication

occurs when using the svn command line tool.
The subversion server is authenticating using kerberos and ldap for
authentication in addition to mod_authz_svn

Commenting out the AuthzSVNAccessFile line in the apache config makes the
problem go away at the cost of turning off fine grained access control.

For the time being I have downgraded to the last working version of the
subversion-server package which is subversion-server-1.8.14-2.20.1

This appears related to
https://subversion.open.collab.net/ds/viewMessage.do?dsMessageId=566035&dsForumId=3

The necessary patch is most likely
http://svn.apache.org/viewvc/subversion/trunk/subversion/mod_authz_svn/mod_authz_svn.c?r1=1695681&r2=1708699