Allow storing information in the JWT

[xixixao]

Some people might be more familiar with retrieving information from the JWT instead of from the DB. The client would provide the equivalent of Clerk's useUser hook, and on the backend await ctx.auth.getUserIdentity() could be used.

[cmaycumber]

This seems import for routing for middleware on NextJS apps as well. Being able to retrieve info from the JWT like an org role would be helpful for determining if a user could visit an admin route before hitting the client.