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How can I inspect a SAML request?

Until recently, I never had to go near SAML with a 10 foot pole but I was recently helping out a coworker with adding SAML authentication to an Elasticsearch cluster.

I had never seen one before but a SAML request looks a little like this:

https://idp.example.org/SAML2/SSO/Redirect?SAMLRequest=fZFfa8IwFMXfBb9DyXvaJtZ1BqsURRC2Mabbw95ivc5Am3TJrXPffmmLY3%2FA15Pzuyf33On8XJXBCaxTRmeEhTEJQBdmr%2FRbRp63K3pL5rPhYOpkVdYib%2FCon%2BC9AYfDQRB4WDvRvWWksVoY6ZQTWlbgBBZik9%2FfCR7GorYGTWFK8pu6DknnwKL%2FWEetlxmR8sBHbHJDWZqOKGdsRJM0kfQAjCUJ43KX8s78ctnIz%2Blp5xpYa4dSo1fjOKGM03i8jSeCMzGevHa2%2FBK5MNo1FdgN2JMqPLmHc0b6WTmiVbsGoTf5qv66Zq2t60x0wXZ2RKydiCJXh3CWVV1CWJgqanfl0%2Bin8xutxYOvZL18NKUqPlvZR5el%2BVhYkAgZQdsA6fWVsZXE63W2itrTQ2cVaKV2CjSSqL1v9P%2FAXv4C

I took this example from Wikipedia and it’s a pretty good illustration of where the juicy part of the request probably is.

A basic way to inspect this request in Python would look like the following. I don’t claim that this will work on all requests. For that, try something like python3-saml.

from base64 import b64decode
from urllib.parse import unquote
import zlib

url = "fZFfa8IwFMXfBb9DyXvaJtZ1BqsURRC2Mabbw95ivc5Am3TJrXPffmmLY3%2FA15Pzuyf33On8XJXBCaxTRmeEhTEJQBdmr%2FRbRp63K3pL5rPhYOpkVdYib%2FCon%2BC9AYfDQRB4WDvRvWWksVoY6ZQTWlbgBBZik9%2FfCR7GorYGTWFK8pu6DknnwKL%2FWEetlxmR8sBHbHJDWZqOKGdsRJM0kfQAjCUJ43KX8s78ctnIz%2Blp5xpYa4dSo1fjOKGM03i8jSeCMzGevHa2%2FBK5MNo1FdgN2JMqPLmHc0b6WTmiVbsGoTf5qv66Zq2t60x0wXZ2RKydiCJXh3CWVV1CWJgqanfl0%2Bin8xutxYOvZL18NKUqPlvZR5el%2BVhYkAgZQdsA6fWVsZXE63W2itrTQ2cVaKV2CjSSqL1v9P%2FAXv4C"
urldecoded_url = unquote(url)
b64decoded_url = b64decode(url)
request = zlib.decompress(b64decoded_url, -15).decode()
print(request) // '<?xml version="1.0" encoding="UTF-8"?>\r\n<samlp:AuthnRequest\r\n  xmlns:samlp="urn:oasis:names:tc:SAML:2.0:protocol"\r\n  xmlns:saml="urn:oasis:names:tc:SAML:2.0:assertion"\r\n  ID="aaf23196-1773-2113-474a-fe114412ab72"\r\n  Version="2.0"\r\n  IssueInstant="2004-12-05T09:21:59Z"\r\n  AssertionConsumerServiceIndex="0"\r\n  AttributeConsumingServiceIndex="0">\r\n  <saml:Issuer>https://sp.example.com/SAML2</saml:Issuer>\r\n  <samlp:NameIDPolicy\r\n    AllowCreate="true"\r\n    Format="urn:oasis:names:tc:SAML:2.0:nameid-format:transient"/>\r\n</samlp:AuthnRequest>\r\n'

If you’re feeling a bit lazy, like I often am, you can use any of the online decoders, such as this one by PingID.

If you’re dealing with sensitive credentials however, it’s best to decode it locally rather than trusting a third party.