verify, go back to Oasis.Token module for more information.
An optional callback function to decode the original data from the token, and verify its integrity.
If we use
sign/2 to create a token, sign it, then provide it to a client application,
the client will then use this token to authenticate requests for resources from the server,
in this scenario, as a common use case, the
Oasis.Plug.BearerAuth module uses
to finish the verification of the bearer token, so we do not need to implement this
callback function in general.
But if we use
encrypt/2 or other encryption methods to encode, encrypt, and sign data into a token
and send to clients, we need to implement this callback function to custom the way to decrypt
the token and verify its integrity.