access_key isn't in the format standard header 

This is somewhat of a feature request rather than an issue, as I'm able to work around it.  'access_key' isn't in a standard canonical header format, which means that some http libraries reformat it.  Headers ought to be case insensitive (https://www.w3.org/Protocols/rfc2616/rfc2616-sec4.html#sec4.2), so it would be nice if the API also recognised Access-Key as well as access_key