The GNOME keyring password provider can return the error "GNOME keyring is
locked and we are non-interactive". This happens when a password is stored in
the keyring but cannot be obtained because the keyring is locked and Subversion
is unable to prompt to unlock the keyring because the user requested
non-interactive operation. The inability to obtain the password causes
authentication to fail and the GNOME error explains why it failed.
In libsvn_ra_neon/session.c:request_auth any error returned by the provider is
cleared and a generic -1 returned, so the special GNOME error is not returned to
the client. In contrast ra_svn and ra_serf both pass on the GNOME error and so
it is visible to the user.