Verifying reCAPTCHA with Erlang

recaptcha.erl

-module(recaptcha).
-export([verify/3]).

-define(PRIVATE_KEY, "YOU_RPRIVATE_KEY").
-define(URL, "http://www.google.com/recaptcha/api/verify").

%% @doc WARNING: 'inets' application should be started!
-spec verify(list(), list(), list()) -> ok |
        {error, invalid_site_private_key | invalid_request_cookie |
            incorrect_captcha_sol}.
verify(Challenge, Response, RemoteIp) ->
    Params = "privatekey=" ++ ?PRIVATE_KEY ++ "&challenge=" ++ Challenge ++
        "&response=" ++ Response ++ "&remoteip=" ++ RemoteIp,
    case httpc:request(post,
            {?URL, [], "application/x-www-form-urlencoded", Params}, [], []) of
        {ok, {_, _, "true\nsuccess"}} -> ok;
        {ok, {_, _, Resp}} -> {error, parse_error(Resp)}
    end.

parse_error("false\ninvalid-site-private-key") -> invalid_site_private_key;
% invalid challenge:
parse_error("false\ninvalid-request-cookie") -> invalid_request_cookie;
parse_error("false\nincorrect-captcha-sol") -> incorrect_captcha_sol.