feat: add fastify example

[songkeys]

The code works good in my machine!

I just finished the example in /dev fold. Pretty much a direct copy paste of your work tbh.

And I noticed reply.session should actually be typed in the plugin itself rather than the user end?

[hillac]

I'll check with the maintainers but I think we probably should leave the session management up to the user given we are having them define their own auth prehandlers. nextauthjs#9587 (comment)

[songkeys]

Ah, I overlooked the part where users need to define the session decorator themselves in their prehandlers. I've reverted that in the next commit.

However, I believe many Fastify plugin libraries within its ecosystem actually define the decorators themselves. For instance, take a look at https://github.com/fastify/fastify-passport. Users can create the auth middleware using a helper from the library:

server.get(
  '/',
  { preValidation: fastifyPassport.authenticate('test', { authInfo: false }) },
  async () => 'hello world!'
)

That said, this could result in duplicated names for decorator properties: fastify/fastify#1955 . But I suppose that's just how things work in the Fastify ecosystem. We can stick to the current design though.

[hillac]

nextauthjs#9587 (comment) Yeah I agree it would be simpler for users but they want to keep it flexible which is also fair.

[songkeys]

@hillac Hi! Could you please take another look? I've corrected the issues. Some mistakes are made because I copied files for the whole auth config from the express folder without double-checking after completing testing.