obtaining AWS credentials using cognito in python boto

Question

I'm trying to emulate the flow of my server application creating a temporary access/secret key pair for a mobile device using my own authentication. Mobile device talks to my server and end result is it gets AWS credentials.

I'm using Cognito with a custom developer backend, see documentation here.

To this end, I've made the script below, but my secret/access key credentials don't work:

import time
import traceback 
from boto.cognito.identity.layer1 import CognitoIdentityConnection
from boto.sts import STSConnection
from boto.s3.connection import S3Connection
from boto.s3.key import Key


AWS_ACCESS_KEY_ID = "XXXXX"
AWS_SECRET_ACCESS_KEY = "XXXXXX"


# get token
iden_pool_id = "us-east-1:xxx-xxx-xxx-xxxx-xxxx"
role_arn = "arn:aws:iam::xxxx:role/xxxxxxx"
user_id = "xxxx"
role_session_name = "my_session_name_here"
bucket_name = 'xxxxxxxxxx'


connection = CognitoIdentityConnection(aws_access_key_id=AWS_ACCESS_KEY_ID, aws_secret_access_key=AWS_SECRET_ACCESS_KEY)

web_identity_token = connection.get_open_id_token_for_developer_identity(
    identity_pool_id=iden_pool_id, 
    logins={"xxxxxxxxx" : user_id}, 
    identity_id=None, 
    token_duration=3600)


# use token to get credentials
sts_conn = STSConnection(aws_access_key_id=AWS_ACCESS_KEY_ID, aws_secret_access_key=AWS_SECRET_ACCESS_KEY)
result = sts_conn.assume_role_with_web_identity(
    role_arn, 
    role_session_name, 
    web_identity_token['Token'], 
    provider_id=None, 
    policy=None, 
    duration_seconds=3600)

print "The user now has an access ID (%s) and a secret access key (%s) and a session/security token (%s)!" % (
    result.credentials.access_key, result.credentials.secret_key, result.credentials.session_token)

# just use any call that tests if these credentials work
from boto.ec2.connection import EC2Connection
ec2 = EC2Connection(result.credentials.access_key, result.credentials.secret_key, security_token=result.credentials.session_token)
wait = 1
cumulative_wait_time = 0
while True:
    try:
        print ec2.get_all_regions()
        break
    except Exception as e:
        print e, traceback.format_exc()
        time.sleep(2**wait)
        cumulative_wait_time += 2**wait
        print "Waited for:", cumulative_wait_time
        wait += 1

My thought with the exponential backoff was that perhaps Cognito takes a while to propagate the new access/secret key pair, and thus I might have to wait (pretty unacceptable if so!).

However, this script runs for a 10 minutes and doesn't succeed, which leads me to believe the problem is something else.

Console print out:

The user now has an access ID (xxxxxxxx) and a secret access key (xxxxxxxxxx) and a session/security token (XX...XX)!

EC2ResponseError: 401 Unauthorized
<?xml version="1.0" encoding="UTF-8"?>
<Response><Errors><Error><Code>AuthFailure</Code><Message>AWS was not able to validate the provided access credentials</Message></Error></Errors><RequestID>xxxxxxxxxx</RequestID></Response> Traceback (most recent call last):
  File "/home/me/script.py", line 50, in <module>
    print ec2.get_all_regions()
  File "/home/me/.virtualenvs/venv/local/lib/python2.7/site-packages/boto/ec2/connection.py", line 3477, in get_all_regions
    [('item', RegionInfo)], verb='POST')
  File "/home/me/.virtualenvs/venv/local/lib/python2.7/site-packages/boto/connection.py", line 1186, in get_list
    raise self.ResponseError(response.status, response.reason, body)
EC2ResponseError: EC2ResponseError: 401 Unauthorized
<?xml version="1.0" encoding="UTF-8"?>
<Response><Errors><Error><Code>AuthFailure</Code><Message>AWS was not able to validate the provided access credentials</Message></Error></Errors><RequestID>xxxxxxxxxxxxx</RequestID></Response>

Waited for: 2
...
...

Any thoughts?

Answer 1

You are correctly extracting the access key and secret key from the result of the assume_role_with_web_identity call. However, when using the temporary credentials, you also need to use the security token from the result.

Here is pseudocode describing what you need to do: http://docs.aws.amazon.com/STS/latest/UsingSTS/using-temp-creds.html#using-temp-creds-sdk

Also note the security_token parameter for EC2Connection http://boto.readthedocs.org/en/latest/ref/ec2.html#boto.ec2.connection.EC2Connection

Hopefully this solves the problem

-Mark