[pysaml2] PySAML2 XML external entity attack

PySAML2 allows remote attackers to conduct XML external entity (XXE) attacks via a crafted SAML XML request or response.
References

https://nvd.nist.gov/vuln/detail/CVE-2016-10127
https://github.com/rohe/pysaml2/issues/366
https://github.com/rohe/pysa…