Basic auth middleware

[tmattio]

This PR adds a basic_auth middleware to protect handlers with an authentication mechanism.

It also adds an Auth module with functions to encode/decode Authorization header values.

The basic_auth middleware has type

val basic_auth
  :  ?unauthorized_handler:Rock.Handler.t
  -> key:'a Context.key
  -> realm:string
  -> auth_callback:(username:string -> password:string -> 'a option)
  -> unit
  -> Rock.Middleware.t

I believe it is flexible enough and will allow users to build their own authentication logic, without having to deal with the boilerplate logic.

TODO

• Document the Auth module
• Support Bearer, and maybe cookie?

[tmattio]

@Jerben I'm curious, do you have any authentication layer in Sihl? If so, would it be compatible with the changes in this PR?

[reynir]

I look over the changes and have some comments about the example, but also how 'other' authentication methods are handled.

[joseferben]

@Jerben I'm curious, do you have any authentication layer in Sihl? If so, would it be compatible with the changes in this PR?

@tmattio At the moment, we have that in the projects themselves. Your approach looks good and we could definitely use the middleware as proposed, I especially like the configurable rock handler 👍

[reynir]

It looks good to me now. Thanks for implementing it! 🎉

[tmattio]

It looks good to me now. Thanks for implementing it!

Thanks for the reviews, appreciate it! I'll investigate further to support Bearer / other auth methods before I merge it: I'm not confident enough that the current implementation generalizes well 🙂