I have created google service account and have JSON file containing private_key
, client_email
etc.
JWT should be created to get access token.
I have followed following step
Header computation:
Header = jsx:encode(#{<<"alg">> => <<"RS256">>,<<"typ">> => <<"JWT">>}).
Base64Header = base64:encode(Header).
Claims computation:
Claims = jsx:encode(#{
<<"iss">> => <<"google-123@some-test.iam.gserviceaccount.com">>,
<<"scope">> => <<"https://www.googleapis.com/auth/cloud-platform">>,
<<"aud">> => <<"https://www.googleapis.com/oauth2/v4/token">>,
<<"exp">> => 1471629262,
<<"iat">> => 1471627282
}).
Base64Claims = base64:encode(Claims).
Input = {Base64Header}.{Base64Claim}
And,
How we can sign the UTF-8 representation of the Input
using SHA256withRSA (also known as RSASSA-PKCS1-V1_5-SIGN with the SHA-256 hash function) with the private_key
to compute JWT Signature?
There are libraries already built to do this. One (which I am using) is Erlang JOSE.
%% In OTP 17 or later
Signed = jose_jwt:sign(RSAPrivate, #{ <<"alg">> => <<"RS256">> }, Payload),
{_JWS, Token} = jose_jws:compact(Signed).