code: private void authorizeClassicDbSecurityGroup(String groupName, String sourceCidr) throws CloudException, InternalException {
          Map<String,String> parameters = getProvider().getStandardRdsParameters(getProvider().getContext(), AUTHORIZE_DB_SECURITY_GROUP_INGRESS);
          parameters.put("DBSecurityGroupName", groupName);
          parameters.put("CIDRIP", sourceCidr);
          EC2Method method = new EC2Method(SERVICE_ID, getProvider(), parameters);
          try {
              method.invoke();
          }
          catch( EC2Exception e ) {
              String code = e.getCode();
              if( code != null && code.equals("AuthorizationAlreadyExists") ) {
                  return;
              }
              throw new CloudException(e);
          }
      }
docs: Use this to authorize with security groups in EC2-Classic
  @param groupName
  @param sourceCidr
  @throws CloudException
  @throws InternalException