How to sign amazon web service requests from the python app engine?

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清歌不尽
清歌不尽 2021-02-06 18:53

I use Amazon web service api from within my Google app engine application. Amazon have said that they will only accept signed requests from Aug 15, 2009. While they have given

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  • 2021-02-06 19:28

    See http://sowacs.appspot.com/AWS/Downloads/#python for a GAE Python signing service webapp. Uses native Python libraries.

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  • 2021-02-06 19:36

    Got this to work based on code sample at http://jjinux.blogspot.com/2009/06/python-amazon-product-advertising-api.html Here is a minor improved version that lets you merge a dict of call specific params with the basic params before making the call.

    keyFile = open('accesskey.secret', 'r')
    # I put my secret key file in .gitignore so that it doesn't show up publicly
    AWS_SECRET_ACCESS_KEY = keyFile.read()
    keyFile.close()
    
    def amz_call(self, call_params):
    
        AWS_ACCESS_KEY_ID = '<your-key>'
        AWS_ASSOCIATE_TAG = '<your-tag>'
    
        import time
        import urllib
        from boto.connection import AWSQueryConnection
        aws_conn = AWSQueryConnection(
            aws_access_key_id=AWS_ACCESS_KEY_ID,
            aws_secret_access_key=Amz.AWS_SECRET_ACCESS_KEY, is_secure=False,
            host='ecs.amazonaws.com')
        aws_conn.SignatureVersion = '2'
        base_params = dict(
            Service='AWSECommerceService',
            Version='2008-08-19',
            SignatureVersion=aws_conn.SignatureVersion,
            AWSAccessKeyId=AWS_ACCESS_KEY_ID,
            AssociateTag=AWS_ASSOCIATE_TAG,
            Timestamp=time.strftime("%Y-%m-%dT%H:%M:%S", time.gmtime()))
        params = dict(base_params, **call_params)
        verb = 'GET'
        path = '/onca/xml'
        qs, signature = aws_conn.get_signature(params, verb, path)
        qs = path + '?' + qs + '&Signature=' + urllib.quote(signature)
        print "verb:", verb, "qs:", qs
        return aws_conn._mexe(verb, qs, None, headers={})
    

    Sample usage:

    result = self.amz_call({'Operation' : 'ItemSearch' , 'Keywords' : searchString , 'SearchIndex' : 'Books' , 'ResponseGroup' : 'Small' })
    if result.status == 200:
        responseBodyText = result.read()
        # do whatever ...
    
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  • 2021-02-06 19:38

    Pycrypto will work fine - it's supported on App Engine, though the public ciphers are implemented in Python rather than C. You also ought to be able to use one of the existing AWS libraries, now that urlfetch/httplib are supported on App Engine.

    I have an app that uploads images to S3, and I've implemented the request signing myself, but mostly because I wrote it before urlfetch/httplib were available. It works just fine, however.

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  • 2021-02-06 19:43

    I use this one using pycrypto to generate a custom policy:

    import json                                                                                                                                                                 
    import time                                                                                                                                                                 
    
    from Crypto.Hash import SHA                                                                                                                                                 
    from Crypto.PublicKey import RSA                                                                                                                                            
    from Crypto.Signature import PKCS1_v1_5                                                                                                                                     
    from base64 import b64encode                                                                                                                                                
    
    url = "http://*"                                                                                                                                                            
    expires = int(time.time() + 3600)
    
    pem = """-----BEGIN RSA PRIVATE KEY-----
    ...
    -----END RSA PRIVATE KEY-----"""
    
    key_pair_id = 'APK.....'
    
    policy = {}                                                                                                                                                                 
    policy['Statement'] = [{}]                                                                                                                                                  
    policy['Statement'][0]['Resource'] = url                                                                                                                                    
    policy['Statement'][0]['Condition'] = {}                                                                                                                                    
    policy['Statement'][0]['Condition']['DateLessThan'] = {}                                                                                                                    
    policy['Statement'][0]['Condition']['DateLessThan']['AWS:EpochTime'] = expires
    
    policy = json.dumps(policy) 
    
    private_key = RSA.importKey(pem)                                                                                                                                            
    policy_hash = SHA.new(policy)                                                                                                                                               
    signer = PKCS1_v1_5.new(private_key)                                                                                                                                        
    signature = b64encode(signer.sign(policy_hash))
    
    print '?Policy=%s&Signature=%s&Key-Pair-Id=%s' % (b64encode(policy),                                                                                                        
                                                      signature,                                                                                                                
                                                      key_pair_id)
    

    This allows me to use one key for multiple items, something like:

    http://your_domain/image1.png?Policy...
    http://your_domain/image2.png?Policy...
    http://your_domain/file1.json?Policy...
    

    Don't forget to enable pycrypto by adding this lines to the app.yaml

    libraries:
    - name: pycrypto
      version: latest 
    
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  • 2021-02-06 19:47

    I wrote another simple example that uses only the core python 3 libraries (not boto) and uses version 2 of the AWS signature protocol:

    http://xocoatl.blogspot.com/2011/03/signing-ec2-api-request-in-python.html

    I know it won't work in GAE, but might be useful for anyone just looking for AWS authentication examples like I was.

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  • 2021-02-06 19:48

    Here is an example of a REST request based on lower level (then boto) libraries. Solution was taken from http://cloudcarpenters.com/blog/amazon_products_api_request_signing.

    All you need is valid entries for AWS_ACCESS_KEY_ID, AWS_SECRET_ACCESS_KEY

    def amazon_test_url():
        import base64, hashlib, hmac, time
        from urllib import urlencode, quote_plus
    
        AWS_ACCESS_KEY_ID = 'YOUR_KEY'
        AWS_SECRET_ACCESS_KEY = 'YOUR_SECRET_KEY'  
        TEST_ISBN = '9780735619678' #http://stackoverflow.com/questions/1711/what-is-the-single-most-influential-book-every-programmer-should-read
    
        base_url = "http://ecs.amazonaws.com/onca/xml"
        url_params = dict(
            Service='AWSECommerceService', 
            Operation='ItemLookup', 
            IdType='ISBN', 
            ItemId=TEST_ISBN,
            SearchIndex='Books',
            AWSAccessKeyId=AWS_ACCESS_KEY_ID,  
            ResponseGroup='Images,ItemAttributes,EditorialReview,SalesRank')
    
        #Can add Version='2009-01-06'. What is it BTW? API version?
    
    
        # Add a ISO 8601 compliant timestamp (in GMT)
        url_params['Timestamp'] = time.strftime("%Y-%m-%dT%H:%M:%SZ", time.gmtime())
    
        # Sort the URL parameters by key
        keys = url_params.keys()
        keys.sort()
        # Get the values in the same order of the sorted keys
        values = map(url_params.get, keys)
    
        # Reconstruct the URL parameters and encode them
        url_string = urlencode(zip(keys,values))
    
        #Construct the string to sign
        string_to_sign = "GET\necs.amazonaws.com\n/onca/xml\n%s" % url_string
    
        # Sign the request
        signature = hmac.new(
            key=AWS_SECRET_ACCESS_KEY,
            msg=string_to_sign,
            digestmod=hashlib.sha256).digest()
    
        # Base64 encode the signature
        signature = base64.encodestring(signature).strip()
    
        # Make the signature URL safe
        urlencoded_signature = quote_plus(signature)
        url_string += "&Signature=%s" % urlencoded_signature
    
        print "%s?%s\n\n%s\n\n%s" % (base_url, url_string, urlencoded_signature, signature)
    
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