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swift-authentication

A modular authentication package that wires Firebase / Apple / Google / REST concretions into a vendor-agnostic core — one target at a time.

Design

Authentication is split into three responsibilities, each defined as a vendor-agnostic protocol. Concrete implementations live in separate targets and are composed at the app's composition root.

AuthenticationStore (@Observable, @MainActor) wires these together and exposes a state property that views observe.

Target Layout

The core (Authentication) and UI (AuthenticationUI) targets have zero vendor SDK dependencies. Views can depend on only these two, keeping SwiftUI Previews free of Firebase / GoogleSignIn. Concrete implementations (Firebase, etc.) are imported only at the composition root.

Installation

dependencies: [
    .package(url: "https://github.com/no-problem-dev/swift-authentication.git", from: "2.0.0")
]

Add only the products your target needs:

• Screen modules → AuthenticationUI (+ Authentication)
• Composition root (App target) → AuthenticationFirebase / AuthenticationApple / AuthenticationGoogle / AuthenticationAPI

Usage

1. Compose AuthenticationStore at the composition root

import SwiftUI
import Authentication
import AuthenticationUI
import AuthenticationFirebase
import AuthenticationApple
import AuthenticationGoogle
import AuthenticationAPI
import APIClient
import FirebaseCore

@main
struct MyApp: App {
    @State private var store: AuthenticationStore

    init() {
        FirebaseConfigurator.configure()   // Production. Use .configure(environment: .emulator()) for local dev.

        let tokenProvider = FirebaseTokenProvider()
        let apiClient = APIClient(
            baseURL: URL(string: "https://api.example.com")!,
            authTokenProvider: APITokenProviderAdapter(tokenProvider)
        )

        let clientID = FirebaseConfigurator.googleClientID ?? ""

        _store = State(initialValue: AuthenticationStore(
            authenticator: FirebaseAuthenticator(),
            postAuthentication: APIUserProvisioning(apiClient: apiClient, path: "/auth/initialize"),
            credentialProviders: [
                AppleCredentialProvider(),
                GoogleCredentialProvider(clientID: clientID)
            ]
        ))
    }

    var body: some Scene {
        WindowGroup {
            AuthenticatedRootView(
                loading: { ProgressView() },
                unauthenticated: {
                    VStack(spacing: 16) {
                        GoogleSignInButton()
                        AppleSignInButton()
                    }
                    .padding(.horizontal, 32)
                },
                error: { error in Text(error.localizedDescription) },
                authenticated: { user in MainView(userID: user.id) }
            )
            .authenticationStore(store)
        }
    }
}

2. Screen views (previewable, vendor-free)

import SwiftUI
import Authentication
import AuthenticationUI

struct MainView: View {
    @Environment(\.authenticationStore) private var store
    let userID: String

    var body: some View {
        VStack {
            Text("Welcome, \(userID)")
            Button("Sign Out") { Task { try? await store?.signOut() } }
        }
    }
}

#Preview {
    // No Firebase needed — uses a stub.
    MainView(userID: "preview")
        .authenticationStore(.previewUnauthenticated)
}

State

AuthenticationState transitions:

• .checking — verifying stored session on launch
• .unauthenticated — no active session
• .authenticatedPendingProvisioning — session exchanged, post-auth action pending
• .authenticated(AuthUser) — fully authenticated
• .error(any Error) — an error occurred

Backend API (optional)

When using APIUserProvisioning, provide a POST <path> endpoint (default /auth/initialize). The Firebase ID token is automatically attached as Authorization: Bearer. The store calls provisioning once per authentication session, but the server endpoint should also be idempotent. If provisioning is not required, omit postAuthentication (defaults to NoPostAuthentication).

Custom Providers

AuthProviderID is open-ended. Implement CredentialProvider / Authenticator / PostAuthenticationAction to plug in any backend — direct Firestore access, custom OIDC, etc.

License

MIT License. See LICENSE for details.