code: def validateRequest(self, uri, postVars, expectedSignature):
          
  
          # append the POST variables sorted by key to the uri
          s = uri
          for k, v in sorted(postVars.items()):
              s += k + v
  
          # compute signature and compare signatures
          return (base64.encodestring(hmac.new(self.auth_token, s, sha1).digest()).\
              strip() == expectedSignature)
docs: validate a request from plivo
  
          uri: the full URI that Plivo requested on your server
          postVars: post vars that Plivo sent with the request
          expectedSignature: signature in HTTP X-Plivo-Signature header
  
          returns true if the request passes validation, false if not