Relevant code blocks:

```
public String getProxyTicketIdFor(final String proxyGrantingTicketId,
                                      final String targetService) {

        final String url = constructUrl(proxyGrantingTicketId, targetService);
        final String response = CommonUtils.getResponseFromServer(url, this.encoding);
        final String error = XmlUtils.getTextForElement(response, "proxyFailure");

        if (CommonUtils.isNotEmpty(error)) {
            logger.debug(error);
            return null;
        }

        return XmlUtils.getTextForElement(response, "proxyTicket");
    }
```