How do you access an authenticated Google App Engine service from a (non-web) python client?

Solution 1:

appcfg.py, the tool that uploads data to App Engine has to do exactly this to authenticate itself with the App Engine server. The relevant functionality is abstracted into appengine_rpc.py. In a nutshell, the solution is:

1. Use the Google ClientLogin API to obtain an authentication token. appengine_rpc.py does this in _GetAuthToken
2. Send the auth token to a special URL on your App Engine app. That page then returns a cookie and a 302 redirect. Ignore the redirect and store the cookie. appcfg.py does this in _GetAuthCookie
3. Use the returned cookie in all future requests.

You may also want to look at _Authenticate, to see how appcfg handles the various return codes from ClientLogin, and _GetOpener, to see how appcfg creates a urllib2 OpenerDirector that doesn't follow HTTP redirects. Or you could, in fact, just use the AbstractRpcServer and HttpRpcServer classes wholesale, since they do pretty much everything you need.

Solution 2:

thanks to Arachnid for the answer - it worked as suggested

here is a simplified copy of the code, in case it is helpful to the next person to try!

import os
import urllib
import urllib2
import cookielib

users_email_address = "[email protected]"
users_password      = "billybobspassword"

target_authenticated_google_app_engine_uri = 'http://mylovelyapp.appspot.com/mylovelypage'
my_app_name = "yay-1.0"



# we use a cookie to authenticate with Google App Engine
#  by registering a cookie handler here, this will automatically store the 
#  cookie returned when we use urllib2 to open http://currentcost.appspot.com/_ah/login
cookiejar = cookielib.LWPCookieJar()
opener = urllib2.build_opener(urllib2.HTTPCookieProcessor(cookiejar))
urllib2.install_opener(opener)

#
# get an AuthToken from Google accounts
#
auth_uri = 'https://www.google.com/accounts/ClientLogin'
authreq_data = urllib.urlencode({ "Email":   users_email_address,
                                  "Passwd":  users_password,
                                  "service": "ah",
                                  "source":  my_app_name,
                                  "accountType": "HOSTED_OR_GOOGLE" })
auth_req = urllib2.Request(auth_uri, data=authreq_data)
auth_resp = urllib2.urlopen(auth_req)
auth_resp_body = auth_resp.read()
# auth response includes several fields - we're interested in 
#  the bit after Auth= 
auth_resp_dict = dict(x.split("=")
                      for x in auth_resp_body.split("\n") if x)
authtoken = auth_resp_dict["Auth"]

#
# get a cookie
# 
#  the call to request a cookie will also automatically redirect us to the page
#   that we want to go to
#  the cookie jar will automatically provide the cookie when we reach the 
#   redirected location

# this is where I actually want to go to
serv_uri = target_authenticated_google_app_engine_uri

serv_args = {}
serv_args['continue'] = serv_uri
serv_args['auth']     = authtoken

full_serv_uri = "http://mylovelyapp.appspot.com/_ah/login?%s" % (urllib.urlencode(serv_args))

serv_req = urllib2.Request(full_serv_uri)
serv_resp = urllib2.urlopen(serv_req)
serv_resp_body = serv_resp.read()

# serv_resp_body should contain the contents of the 
#  target_authenticated_google_app_engine_uri page - as we will have been 
#  redirected to that page automatically 
#
# to prove this, I'm just gonna print it out
print serv_resp_body

Solution 3:

for those who can't get ClientLogin to work, try app engine's OAuth support.