I did some more digging. Having read the SRP documentation, this seems a likely approach. Here is some Python code:
import requests
import srp
import base64
username = 'testuser'
myserver = 'http://127.0.0.1:8080'
r = requests.get(myserver + '/login?username=' + username)
niauthheader = r.headers.get('x-ni-auth-params')
my_fields = niauthheader.split(",")
srpdict = {}
for field in my_fields:
g = field.partition('=')
srpdict[g[0]]=base64.b64decode(g[2])
# srpdict now contains s, B, and ss. NI Auth wants us to return a POST containing
# A,M, and ss. We can snoop what the Silverlight plugin returns given the values for
# s, B, the username and password using a MITM attack (ZAP is good for this). If we
# can replicate the calls to SRP, we should get the same values for A & M. Referring
# to the Python srp 1.05 documentation, the easiest thing to try is:
usr = srp.User( username, 'password' )
uname, A = usr.start_authentication()
M = usr.process_challenge( s, B )
print 'A=' + base64.b64encode(A)
print 'M=' + base64.b64encode(M)
This doesn't result in the snooped values for A & M. Two questions:
1) Is NI using something other than default values for the hash_alg or the ng_type?
2) What is ss? It changes on every call, but it doesn't seem to map to anything in srp.
I have much better things to do with my time that to reverse engineer NI Auth. Much
easier to just handle security myself through Apache, but if NI provided a little bit
of documentation on their implementation, this would be nice. Conversely, if NI permitted
passing an external authentication routine to the web server & http client routines, this
would be even nicer.
