google oauth2

gistfile1.erl

%%%-------------------------------------------------------------------
%%% @author 신원동 <wodshin@gmail.coml>
%%% @copyright (C) 2014, 신원동
%%% @doc
%%%
%%% @end
%%% Created :  4 Dec 2014 by 신원동 <wodshin@gmail.com>
%%%-------------------------------------------------------------------
-module(m_oauth2).


-include_lib("public_key/include/public_key.hrl"). 

%% API
-export([access_token/3]).

%%%===================================================================
%%% API
%%%===================================================================


%%--------------------------------------------------------------------
%% @doc
%% @spec
%% @end
%%--------------------------------------------------------------------


access_token(ISS,Scope,PemFileName) ->
    Payload = jwt(ISS,Scope,PemFileName),

    Headers=[ {"Content-type", "application/x-www-form-urlencoded" } ],

    { RetCode , OpCode, Json , Attachment } = ibrowse:send_req("https://accounts.google.com/o/oauth2/token", Headers , post, Payload , [] ),
    case { RetCode , OpCode } of
        { ok , "200" } ->
            R = jsx:decode(list_to_binary(Attachment)),
            Token = proplists:get_value(<<"access_token">>,R,<<"">>),
            { ok , Token };
        _ ->
            { error , OpCode }
    end.



%%%===================================================================
%%% Internal functions
%%%===================================================================


jwt_header() -> 
    <<"eyJhbGciOiJSUzI1NiIsInR5cCI6IkpXVCJ9">>.

aud() ->
    <<"https://accounts.google.com/o/oauth2/token">>.

exp(IAT) ->
   IAT + 60*60.

iat() ->
    m_util_time:epoch().


jwt_claim_set(ISS,Scope) ->

    IAT = iat(),
    EXP = exp(IAT),

    R = [ { <<"iss">> , ISS } , { <<"scope">> , Scope } , { <<"aud">> , aud() } , { <<"exp">> , EXP } , { <<"iat">> , IAT } ],
    
    Bin = jsx:encode(R),

    base64url:encode(Bin).

get_private_key(PemFileName) ->

    { ok , F } = file:read_file(PemFileName),
    PrivateKeyEntry = public_key:pem_decode(F),
    PrivateKeyEntry1=hd(PrivateKeyEntry),
    PrivateKey = public_key:pem_entry_decode(PrivateKeyEntry1),
    #'RSAPrivateKey'{publicExponent=Exponent
                    ,modulus=Modulus
                    ,privateExponent=PrivateExponent} = PrivateKey,

    [Exponent, Modulus, PrivateExponent].


jwt(ISS,Scope,PemFileName) ->
    
    ToEncrypt = << (jwt_header())/binary , $. , (jwt_claim_set(ISS,Scope))/binary  >>,

    Key = get_private_key(PemFileName),

    S=base64url:encode(crypto:sign(rsa,'sha256',ToEncrypt,Key)),
    << <<"grant_type=urn:ietf:params:oauth:grant-type:jwt-bearer&assertion=">>/binary , ToEncrypt/binary , $. , S/binary >>.