Sounds like the agent was having a bad day. You will always have an old school paper Jumpseat request form. If you need to be CASS approved, the section for that is on the top. If you were in JFK, the help desk can CASS you if the gate agent is busy. Sorry you didn't have a great experince at the gate. Usually, the agents will CASS you right away if there is any question to needing the Jumpseat.