code: public static String getPluginGoalConfigurationString(MavenProject project, String pluginKey, String goal, String configName) throws PluginScenarioException {
          PluginExecution execution = getPluginGoalExecution(project, pluginKey, goal);
          
          final Xpp3Dom config = (Xpp3Dom)execution.getConfiguration();
          if(config != null) {
              Xpp3Dom configElement = config.getChild(configName);
              if(configElement != null) {
                  String value = configElement.getValue().trim();
                  return value;
              }
          }
          throw new PluginScenarioException("Could not find configuration string " + configName + " for goal " + goal + " on plugin " + pluginKey);
      }
docs: Get a configuration value from a goal from a plugin
  @param project
  @param pluginKey
  @param goal
  @param configName
  @return the value of the configuration parameter
  @throws PluginScenarioException