Add ability to encrypt payload (for Wingate11)

[msmiller]

The key will be stored in the Federation objects, so each instance will need to know each other's keys to properly handle encryption. But this means that if someone does bust into the Redis server, they won't be able to do anything with the raw data.

key = SecureRandom.random_bytes(32)
crypt = ActiveSupport::MessageEncryptor.new(key) 
encrypted_data = crypt.encrypt_and_sign('my confidential data') 

decrypted_back = crypt.decrypt_and_verify(encrypted_data)