# pyAWS no longer works with the AWS signed request requirement
# Sign an AWS REST request using the method described here
# http://docs.amazonwebservices.com/AWSECommerceService/latest/DG/index.html?RequestAuthenticationArticle.html
#_______________________________________________________________________________
def getSignedUrl(accessKey, secretKey, params):
 
    #Step 0: add accessKey, Service, Timestamp, and Version to params
    params['AWSAccessKeyId'] = accessKey
    params['Service']        = 'AWSECommerceService'
 
    #Amazon adds hundredths of a second to the timestamp (always .000), so we do too.
    #(see http://associates-amazon.s3.amazonaws.com/signed-requests/helper/index.html)
    params['Timestamp']      = time.strftime("%Y-%m-%dT%H:%M:%S.000Z", time.gmtime())
    params['Version']        = '2009-03-31'
 
    #Step 1a: sort params
    paramsList = params.items()
    paramsList.sort()
 
    #Step 1b-d: create canonicalizedQueryString
    # This code comes from http://blog.umlungu.co.uk/blog/2009/jul/12/pyaws-adding-request-authentication/
    # and the resulting discussion
    canonicalizedQueryString = '&'.join(['%s=%s' % (k,urllib.quote(str(v))) for (k,v) in paramsList if v])
 
    #Step 2: create string to sign
    host          = 'ecs.amazonaws.com'
    requestUri    = '/onca/xml'
    stringToSign  = 'GET\n'
    stringToSign += host +'\n'
    stringToSign += requestUri+'\n'
    stringToSign += canonicalizedQueryString.encode('utf-8')
 
    #Step 3: create HMAC
    digest = hmac.new(secretKey, stringToSign, hashlib.sha256).digest()
 
    #Step 4: base64 the hmac
    sig = base64.b64encode(digest)
 
    #Step 5: append signature to query
    url  = 'http://' + host + requestUri + '?'
    url += canonicalizedQueryString + "&Signature=" + urllib.quote(sig)
 
    return url