Hudson does rewrite the authentication file under ${user.home}/.subversion/auth/svn.simple/$file and does not insert credentials stuff.
I am using a custom build which does use the command line client (in addition to the normal svn usage of the hudson project) - so the credentials are important to be in there. My custom project is broken every time hudson does rewrite those authentication cache file from subversion.

Is it possible to configure hudson not to do this rewrite or to insert those credentials when the rewrite does happen?

The only workaround found is to set the immutable bit (removing write privileges is not enough) as root user to the file in question which hudson is not able to workaround (which is expected here and good).
Project does build but the log grows with these exception trace:

Nov 10, 2010 10:54:47 AM hudson.scm.SubversionSCM$CheckOutTask invoke
INFO: Failed to estimate the remote time stamp
org.tmatesoft.svn.core.SVNException: svn: Cannot rename file '/home/hudson/.subversion/auth/svn.simple/auth.d17e3535-2c01-0010-81b2-1f57b38e3f1e.tmp' to '/home/hudson/.subversion/auth/svn.simple/1755861b3f63d264955a25532195c4f8'
at org.tmatesoft.svn.core.internal.wc.SVNErrorManager.error(SVNErrorManager.java:64)
at org.tmatesoft.svn.core.internal.wc.SVNFileUtil.rename(SVNFileUtil.java:552)
at org.tmatesoft.svn.core.internal.wc.SVNWCProperties.setProperties(SVNWCProperties.java:352)
at org.tmatesoft.svn.core.internal.wc.DefaultSVNAuthenticationManager$PersistentAuthenticationProvider.saveAuthentication(DefaultSVNAuthenticationManager.java:810)
at org.tmatesoft.svn.core.internal.wc.DefaultSVNAuthenticationManager.acknowledgeAuthentication(DefaultSVNAuthenticationManager.java:276)
at org.tmatesoft.svn.core.internal.io.dav.http.HTTPConnection.request(HTTPConnection.java:606)
at org.tmatesoft.svn.core.internal.io.dav.http.HTTPConnection.request(HTTPConnection.java:275)
at org.tmatesoft.svn.core.internal.io.dav.http.HTTPConnection.request(HTTPConnection.java:263)
at org.tmatesoft.svn.core.internal.io.dav.DAVConnection.exchangeCapabilities(DAVConnection.java:516)
at org.tmatesoft.svn.core.internal.io.dav.DAVConnection.open(DAVConnection.java:98)
at org.tmatesoft.svn.core.internal.io.dav.DAVRepository.openConnection(DAVRepository.java:1001)
at org.tmatesoft.svn.core.internal.io.dav.DAVRepository.info(DAVRepository.java:724)
at hudson.scm.SubversionSCM$CheckOutTask.invoke(SubversionSCM.java:698)
at hudson.scm.SubversionSCM$CheckOutTask.invoke(SubversionSCM.java:596)
at hudson.FilePath.act(FilePath.java:753)
at hudson.FilePath.act(FilePath.java:735)
at hudson.scm.SubversionSCM.checkout(SubversionSCM.java:589)
at hudson.scm.SubversionSCM.checkout(SubversionSCM.java:537)
at hudson.model.AbstractProject.checkout(AbstractProject.java:1119)
at hudson.model.AbstractBuild$AbstractRunner.checkout(AbstractBuild.java:479)
at hudson.model.AbstractBuild$AbstractRunner.run(AbstractBuild.java:411)
at hudson.model.Run.run(Run.java:1324)
at hudson.model.FreeStyleBuild.run(FreeStyleBuild.java:46)
at hudson.model.ResourceController.execute(ResourceController.java:88)
at hudson.model.Executor.run(Executor.java:139)

Of cause it can not rename the file, the immutable bit is set and only the root user is able to change this or any process which got the CAP_LINUX_IMMUTABLE capability bit set - of cause my hudson process does not get this privilege.

So anything i can do to get rid of those subversion problem without this "workaround"?