How to generate JWS in R language

Question

I try to generate JWT for google-oauth2.0 ServiceAccount.

I set up header and payload (claim). But when I try to sigh base64header.base64claim with RSASHA256 I get incorrect signature. I found only one function in PKI package that alows to sign contet with RSA with specified hash function.

How did I figure that my signature incorrect? I found resource that can generate JWT from inputs and private KEY.

So all I can see, that my signture from R functions differs from jwt.io signature. I've tested requests for https://www.googleapis.com/oauth2/v3/token with both of JWT tokens, and jwt.io one was working.

This part is for JWT header.

library(base64enc)
library(jsonlite)
library(PKI)
#JWT header set up
    alg <- "RS256"
    typ <- "JWT"
    header <- list("alg" = alg, "typ" = typ)
    h <- toJSON(header, auto_unbox=TRUE)
    enc.header <- base64encode(charToRaw(h))

This part is for JWT claim (payload)

iss <- "165724828594-mkuchqogmjapbl7mpfn0e7f7o3qlrqsr@developer.gserviceaccount.com"
        scope <- "https://www.googleapis.com/auth/analytics.readonly"
    aud <- "https://www.googleapis.com/oauth2/v3/token"
    iat <- as.integer(as.POSIXct(Sys.time()))
    exp <- iat+3600
    claim <- list("iss" = iss, "scope" = scope, "aud" = aud, "exp" = exp, "iat" = iat)
    cl <- toJSON(claim, auto_unbox=TRUE)
    enc.claim <- base64encode(charToRaw(cl))

And this is my problem.

y <- file("~/keys/euroset-test-70c2d0d4eed1.pem")
key <- PKI.load.key(y)
what <- paste(enc.header,enc.claim, sep=".")
JWS <- PKI.sign(what, key, "SHA256")
enc.sign <- base64encode(JWS)
JWT <- paste(what,enc.sign, sep=".")
JWT

Any help, please? I've stucked with JWS for 4 days already.(

Answer 1

Finally I've found a problem place. It's always been about base64encoding. I've checked Correct and Inctorrect JWTs and found some pattern. Incorrect one have had "==" in payload and signature, I've replaced it with "" . Also in signature all "/" I've replaced with "_" , and all "+" with "-" . Hope it will give a hint to peopple with the same issue.

Answer 2

https://github.com/hadley/httr/blob/master/R/oauth-server-side.R

This is the code for getting the token which works for some of the Google APIs (but not for the cloud which is what I need.. let me know if you got it working). Also, the httr oauth_service_token is a lot easier to use than coding your own.

init_oauth_service_account <- function(endpoint, secrets, scope = NULL) {
  signature <- jwt_signature(secrets, scope = scope)

  res <- POST(endpoint$access, body = list(
    grant_type = "urn:ietf:params:oauth:grant-type:jwt-bearer",
    assertion = signature
  ), encode = "form")
  stop_for_status(res)

  content(res, type = "application/json")
}
...
jwt_base64 <- function(x) base64url(jwt_json(x))
jwt_json <- function(x) jsonlite::toJSON(x, auto_unbox = TRUE)
base64url <- function(x) {
  if (is.character(x)) {
    x <- charToRaw(x)
  }
  out <- chartr('+/', '-_', base64enc::base64encode(x))
  gsub("=+$", "", out)
}