@Override
        public CancelDelegationTokenResponse cancelDelegationToken(CancelDelegationTokenRequest request)
                throws IOException {
            if (!isAllowedDelegationTokenOp()) {
                throw new IOException("Delegation Token can be cancelled only with kerberos authentication");
            }

            org.apache.hadoop.yarn.api.records.Token protoToken = request.getDelegationToken();
            Token<MRDelegationTokenIdentifier> token = new Token<MRDelegationTokenIdentifier>(
                    protoToken.getIdentifier().array(),
                    protoToken.getPassword().array(),
                    new Text(protoToken.getKind()),
                    new Text(protoToken.getService()));

            String user = UserGroupInformation.getCurrentUser().getUserName();
            jhsDTSecretManager.cancelToken(token, user);
            return Records.newRecord(CancelDelegationTokenResponse.class);
        }
This module is responsible for talking to the
JobClient (user facing).
history-server/src/main/java/net/qihoo/hbox/jobhistory/HistoryClientService.java