protected String getBaseUrl() {
        return service.getAppInstance().getBaseUrl();
    }
This method is used to create a SSORequestOperation.
If the third-part AppConn wants to use SSORequestOperation which dependents the HttpClient of Linkis
to request the third-part system, please override this method. Otherwise, the operations of
third-part AppConn has no necessity to override this method.
@return the appConn name
dss-standard/sso-standard/sso-integration-standard/src/main/java/com/webank/wedatasphere/dss/standard/app/sso/operation/AbstractOperation.java