'Select the headers from the request that need to be included
in the StringToSign.'

def headers_to_sign(self, http_request):

    headers_to_sign = {'Host': self.host}
    for (name, value) in http_request.headers.items():
        lname = name.lower()
        if lname.startswith('x-amz'):
            headers_to_sign[name] = value
    return headers_to_sign
