Configuring dependencies at runtime, eg tokens for URLRoutingClient

[kamcma]

URLRoutingClient from swift-url-routing is quite testable with its override(_:with:) methods. This makes it very tempting to use directly in a TCA environment, particularly in the new concurrency-beta branch, without the overhead of wrapping. My complication comes when I'd like to integrate OAuth token refreshing functionality.

In particular, constructing a live implementation like this would be very cool:

import AppAuth
import URLRouting

extension URLRoutingClient {
  static func appAuthLive<R: ParserPrinter>(
    router: R,
    session: URLSession = .shared,
    decoder: JSONDecoder = .init(),
    authState: OIDAuthState
  ) -> Self where R.Input == URLRequestData, R.Output == Route {
    return Self(
      request: { route in
        let (token, _): (String, String) = try await withCheckedThrowingContinuation { continuation in
          authState.performAction { (token: String?, id: String?, error: Error?) in
            guard
              let token = token,
              let id = id
            else {
              continuation.resume(throwing: error ?? OIDErrorUtilities.error(with: .tokenRefreshError, underlyingError: error, description: nil))
              return
            }
            continuation.resume(returning: (token, id))
          }
        }

        let request = try router
          .baseRequestData(.init(headers: ["Authorization": ["Bearer \(token)"]]))
          .request(for: route)

        return try await session.data(for: request)
      },
      decoder: decoder
    )
  }
}

If you're not familiar with the AppAuth library, the OIDAuthState object holds your OAuth token. Its performAction() method will either give you your token, or refresh it if necessary. I believe it has some internal synchronization logic to not have more than one refresh request in flight, no matter how many times you call .performAction() in quick succession.

My question isn't about AppAuth per se; you could use any OAuth logic or library of your choice. My question is: OIDAuthState won't exist on first launch, or after a logout, so I don't think I can statically configure URLRoutingClient like this. I understand from discussions elsewhere, eg #721, the environment is supposed to be a static set of dependencies. Does that foreclose abstracting away token logic like this? Ideally, I'd like it to be an implementation detail of the client dependency; I'm not really interested in it vis-à-vis my business logic, at least down in the child features downstream of being logged in.

I think I'm approaching this slightly wrong, and would be glad if anyone had any clarifying pointers, or maybe an alternate approach to achieve a similar end. Thanks!

[nayooti]

Maybe this answer helps.

#759