@Override
  public void preCreateTable(ObserverContext<MasterCoprocessorEnvironment> ctx, TableDescriptor htd,
    RegionInfo[] regions) throws IOException {
    verifyCoprocessors(ctx, htd);
  }
Master observer for restricting coprocessor assignments.
hbase-server/src/main/java/org/apache/hadoop/hbase/security/access/CoprocessorWhitelistMasterObserver.java