Jesus called the twelve, and began to send them out in pairs, giving them authority over unclean spirits. Mark 6:7

How do you imagine this exchange took place?
How did the disciples “receive”
authority?
Did Jesus hand them a badge or give then papers with proof authorization?
How did authority come to rest on the disciples?

I think that the only logical answer is that it came through the mere words of Jesus. The statement “I grant you authority” from someone who possess authority must be enough.

The Gospels state that Jesus granted His disciples authority for healing sickness and casting our demons several times. Why? Because disciples for generations to come would need to know that they are granted authority for doing the works of Jesus.

I am a disciple.
I have authority.
Jesus said so.
It’s that simple.