TokenUtil com RestAssured
private static Response authRequest(String username, String password) throws Exception {
return given()
.auth()
.preemptive()
.basic("myclientid", "myclientsecret")
//contentType extamente o que estamos passando na requisição de login
//do Postman (no body)
.contentType("application/x-www-form-urlencoded")
.formParam("grant-type", "password")
.formParam("username", username)
.formParam("username", password)
.when()
.post("/oauth2/token");
}


Atualizado