Implementing User Authentication with Sign in with StackExchange

AppScript/Package.swift

@@ -27,15 +27,19 @@ fileprivate extension Target {
 fileprivate extension Package {
 
     static var dependencies: [Dependency] {
-        externalDependencies + serviceDependencies + storeDependencies
+        [.package(name: "Common", path: "../Common")]
+            + externalDependencies
+            + serviceDependencies
+            + storeDependencies
     }
 
     static var externalDependencies: [Dependency] {
         [.package(name: "Swinject", url: "https://github.com/Swinject/Swinject.git", from: "2.7.1")]
     }
 
     static var serviceDependencies: [Dependency] {
-        [.package(name: "StackexchangeNetworkService", path: "../Services/StackexchangeNetworkService")]
+        [.package(name: "StackexchangeNetworkService", path: "../Services/StackexchangeNetworkService"),
+         .package(name: "AuthManager", path: "../Services/AuthManager")]
     }
 
     static var storeDependencies: [Dependency] {

AppScript/Sources/AppScript/Services.swift

@@ -8,6 +8,8 @@
 
 import Swinject
 import StackexchangeNetworkService
+import AuthManager
+import class Common.StackexchangeAuthConfigurations
 import class PageStore.PageDataManager
 
 // MARK: - Services Assembly
@@ -19,6 +21,10 @@ final class ServicesAssembly: Assembly {
             StackexchangeNetworkService()
         }.inObjectScope(.weak)
 
+        container.register(AuthManager.self) { resolver in
+            AuthManager(configurations: try! StackexchangeAuthConfigurations.load())
+        }.inObjectScope(.weak)
+
         container.register(PageDataManager.self) { resolver in
             PageDataManager(service: resolver.resolve(StackexchangeNetworkService.self)!)
         }.inObjectScope(.weak)
@@ -39,3 +45,12 @@ public struct ServicesAssembler {
         ])
     }()
 }
+
+// MARK: - Extensions
+
+public extension AuthManager {
+
+    static func appearance() -> Self {
+        ServicesAssembler.shared.resolve(Self.self)!
+    }
+}

Application/Info.plist

@@ -16,6 +16,19 @@
 	<string>$(PRODUCT_BUNDLE_PACKAGE_TYPE)</string>
 	<key>CFBundleShortVersionString</key>
 	<string>$(MARKETING_VERSION)</string>
+	<key>CFBundleURLTypes</key>
+	<array>
+		<dict>
+			<key>CFBundleTypeRole</key>
+			<string>Viewer</string>
+			<key>CFBundleURLName</key>
+			<string>com.ephedra-software.StackOv</string>
+			<key>CFBundleURLSchemes</key>
+			<array>
+				<string>stackov</string>
+			</array>
+		</dict>
+	</array>
 	<key>CFBundleVersion</key>
 	<string>$(CURRENT_PROJECT_VERSION)</string>
 	<key>LSApplicationCategoryType</key>

Common/Package.swift

@@ -12,7 +12,9 @@ let package = Package(
     ],
     dependencies: Package.dependencies,
     targets: [
-        .target(name: "Common", dependencies: Target.dependencies),
+        .target(name: "Common",
+                dependencies: Target.dependencies,
+                resources: [.process("Resources/StackexchangeAuthConfigurations.json")]),
         .testTarget(name: "CommonTests", dependencies: ["Common"])
     ]
 )
@@ -27,7 +29,7 @@ fileprivate extension Package {
 fileprivate extension Target {
 
     static var dependencies: [Dependency] {
-        var packages: [Dependency] = ["Introspect"]
+        var packages: [Dependency] = ["URLBuilder", "Introspect"]
         if Package.firebaseIsEnable {
             packages.append(.product(name: "FirebaseCrashlytics", package: "Firebase"))
         }
@@ -43,6 +45,7 @@ fileprivate extension Package {
 
     static var externalDependencies: [Dependency] {
         var packages: [Dependency] = [
+            .package(name: "URLBuilder", url: "https://github.com/ephedra-software/URLBuilder.git", from: "1.0.3"),
             .package(name: "Introspect", url: "https://github.com/Puasonych/SwiftUI-Introspect.git", .branch("develop"))
         ]
         if Package.firebaseIsEnable {

Common/Sources/Common/Configurations/StackexchangeAuthConfigurations.swift

@@ -0,0 +1,54 @@
+//
+//  StackexchangeAuthConfigurations.swift
+//  StackOv (Common module)
+//
+//  Created by Erik Basargin
+//  Copyright © 2021 Erik Basargin. All rights reserved.
+//
+
+import Foundation
+import URLBuilder
+
+public final class StackexchangeAuthConfigurations: Codable {
+
+    // MARK: - Nested types
+
+    public enum CodingKeys: String, CodingKey {
+        case clientId = "client_id"
+        case scope
+        case redirectUri = "redirect_uri"
+    }
+
+    public enum Errors: Error {
+        case confFileNotFound
+    }
+
+    // MARK: - Public properties
+
+    public let clientId: Int
+    public let scope: String
+    public let redirectUri: URL
+
+    // MARK: - Public methods
+
+    public static func load() throws -> Self {
+        guard let filePath = Bundle.module.url(forResource: "\(Self.self)", withExtension: "json") else {
+            throw Errors.confFileNotFound
+        }
+        let data = try Data(contentsOf: filePath)
+        let object = try JSONDecoder().decode(Self.self, from: data)
+        return object
+    }
+
+    public func getAuthUri(host: String) -> URL {
+        URLBuilder.scheme(.https)
+            .host(custom: host)
+            .path(custom: "/oauth/dialog")
+            .query(items: [
+                (CodingKeys.clientId.rawValue, "\(clientId)"),
+                (CodingKeys.scope.rawValue, scope),
+                (CodingKeys.redirectUri.rawValue, redirectUri.absoluteString)
+            ])
+            .url!
+    }
+}

Common/Sources/Common/Resources/StackexchangeAuthConfigurations.json

@@ -0,0 +1,5 @@
+{
+    "client_id": 18018,
+    "scope": "read_inbox,write_access,private_info,no_expiry",
+    "redirect_uri": "stackov://stackexchange.com/oauth/login_success"
+}

Services/AuthManager/.swiftpm/xcode/xcshareddata/xcschemes/AuthManager.xcscheme

@@ -0,0 +1,77 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<Scheme
+   LastUpgradeVersion = "1240"
+   version = "1.3">
+   <BuildAction
+      parallelizeBuildables = "YES"
+      buildImplicitDependencies = "YES">
+      <BuildActionEntries>
+         <BuildActionEntry
+            buildForTesting = "YES"
+            buildForRunning = "YES"
+            buildForProfiling = "YES"
+            buildForArchiving = "YES"
+            buildForAnalyzing = "YES">
+            <BuildableReference
+               BuildableIdentifier = "primary"
+               BlueprintIdentifier = "AuthManager"
+               BuildableName = "AuthManager"
+               BlueprintName = "AuthManager"
+               ReferencedContainer = "container:">
+            </BuildableReference>
+         </BuildActionEntry>
+      </BuildActionEntries>
+   </BuildAction>
+   <TestAction
+      buildConfiguration = "Debug"
+      selectedDebuggerIdentifier = "Xcode.DebuggerFoundation.Debugger.LLDB"
+      selectedLauncherIdentifier = "Xcode.DebuggerFoundation.Launcher.LLDB"
+      shouldUseLaunchSchemeArgsEnv = "YES">
+      <Testables>
+         <TestableReference
+            skipped = "NO">
+            <BuildableReference
+               BuildableIdentifier = "primary"
+               BlueprintIdentifier = "AuthManagerTests"
+               BuildableName = "AuthManagerTests"
+               BlueprintName = "AuthManagerTests"
+               ReferencedContainer = "container:">
+            </BuildableReference>
+         </TestableReference>
+      </Testables>
+   </TestAction>
+   <LaunchAction
+      buildConfiguration = "Debug"
+      selectedDebuggerIdentifier = "Xcode.DebuggerFoundation.Debugger.LLDB"
+      selectedLauncherIdentifier = "Xcode.DebuggerFoundation.Launcher.LLDB"
+      launchStyle = "0"
+      useCustomWorkingDirectory = "NO"
+      ignoresPersistentStateOnLaunch = "NO"
+      debugDocumentVersioning = "YES"
+      debugServiceExtension = "internal"
+      allowLocationSimulation = "YES">
+   </LaunchAction>
+   <ProfileAction
+      buildConfiguration = "Release"
+      shouldUseLaunchSchemeArgsEnv = "YES"
+      savedToolIdentifier = ""
+      useCustomWorkingDirectory = "NO"
+      debugDocumentVersioning = "YES">
+      <MacroExpansion>
+         <BuildableReference
+            BuildableIdentifier = "primary"
+            BlueprintIdentifier = "AuthManager"
+            BuildableName = "AuthManager"
+            BlueprintName = "AuthManager"
+            ReferencedContainer = "container:">
+         </BuildableReference>
+      </MacroExpansion>
+   </ProfileAction>
+   <AnalyzeAction
+      buildConfiguration = "Debug">
+   </AnalyzeAction>
+   <ArchiveAction
+      buildConfiguration = "Release"
+      revealArchiveInOrganizer = "YES">
+   </ArchiveAction>
+</Scheme>

Services/AuthManager/Package.swift

@@ -0,0 +1,20 @@
+// swift-tools-version:5.3
+// The swift-tools-version declares the minimum version of Swift required to build this package.
+
+import PackageDescription
+
+let package = Package(
+    name: "AuthManager",
+    platforms: [.iOS(.v14), .macOS(.v10_15)],
+    products: [
+        .library(name: "AuthManager", targets: ["AuthManager"])
+    ],
+    dependencies: [
+        .package(path: "../Common"),
+        .package(path: "../Network")
+    ],
+    targets: [
+        .target(name: "AuthManager", dependencies: ["Common", "Network"]),
+        .testTarget(name: "AuthManagerTests", dependencies: ["AuthManager"])
+    ]
+)

Services/AuthManager/README.md

@@ -0,0 +1,3 @@
+# AuthManager
+
+A description of this package.

Services/AuthManager/Sources/AuthManager/AuthManager.swift

@@ -0,0 +1,100 @@
+//
+//  AuthManager.swift
+//  StackOv (AuthManager module)
+//
+//  Created by Erik Basargin
+//  Copyright © 2021 Erik Basargin. All rights reserved.
+//
+
+import Foundation
+import AuthenticationServices
+import Common
+import Combine
+
+#if canImport(AppKit) && !targetEnvironment(macCatalyst)
+public typealias ASPresentationAnchor = NSWindow
+#else
+public typealias ASPresentationAnchor = UIWindow
+#endif
+
+final public class AuthManager: NSObject, ObservableObject, ASWebAuthenticationPresentationContextProviding {
+
+    // MARK: - Nested types
+
+    enum Constants {
+        static let accessTokenKey = "access_token"
+    }
+
+    public enum Errors: Error {
+        case unexpectedError
+        case invalidAccessTokenUrl
+        case accessTokenNotFound
+    }
+
+    // MARK: - Properties
+
+    let configurations: StackexchangeAuthConfigurations
+    var authProcess: AnyCancellable?
+
+    // MARK: - Initialization and deinitialization
+
+    public init(configurations: StackexchangeAuthConfigurations) {
+        self.configurations = configurations
+    }
+
+    // MARK: - Public methods
+
+    public func singIn() {
+        authProcess?.cancel()
+        authProcess = Future<URL, Error> { [unowned self] completion in
+            let authUrl = configurations.getAuthUri(host: "stackoverflow.com")
+
+            let authSession = ASWebAuthenticationSession(url: authUrl, callbackURLScheme: nil) { url, error in
+                if let error = error {
+                    completion(.failure(error))
+                } else if let url = url {
+                    completion(.success(url))
+                } else {
+                    completion(.failure(Errors.unexpectedError))
+                }
+            }
+            authSession.presentationContextProvider = self
+            authSession.prefersEphemeralWebBrowserSession = true
+            authSession.start()
+        }
+        .tryMap { [unowned self] url in
+            return try extractToken(fromUrl: url)
+        }
+        .sink { result in
+            if case let .failure(error) = result {
+                // show banner with error
+                print(error)
+            }
+        } receiveValue: { accessToken in
+            print(accessToken)
+            // keep access_token in the keychain
+        }
+    }
+
+    // MARK: - Internal methods
+
+    func extractToken(fromUrl url: URL) throws -> String {
+        guard url.absoluteString.hasPrefix(configurations.redirectUri.absoluteString),
+              var components = URLComponents(url: url, resolvingAgainstBaseURL: true) else {
+            throw Errors.invalidAccessTokenUrl
+        }
+        components.query = components.fragment
+        components.fragment = nil
+        if let accessToken = components.queryItems?.first(where: { $0.name == Constants.accessTokenKey })?.value {
+            return accessToken
+        }
+        throw Errors.accessTokenNotFound
+    }
+
+    // MARK: - ASWebAuthenticationPresentationContextProviding
+
+    @objc
+    public func presentationAnchor(for session: ASWebAuthenticationSession) -> ASPresentationAnchor {
+        return ASPresentationAnchor()
+    }
+}

Services/AuthManager/Tests/AuthManagerTests/AuthManagerTests.swift

@@ -0,0 +1,24 @@
+import XCTest
+import Common
+@testable import AuthManager
+
+final class AuthManagerTests: XCTestCase {
+
+    func testAccessTokenExtractor() {
+        do {
+            let config = try StackexchangeAuthConfigurations.load()
+            let manager = AuthManager(configurations: config)
+            let tokenValue = "{access_token_value}"
+            let url: URL = {
+                var components = URLComponents(url: config.redirectUri, resolvingAgainstBaseURL: true)!
+                components.fragment = "access_token=\(tokenValue)"
+                return components.url!
+            }()
+
+            let extractedToken = try manager.extractToken(fromUrl: url)
+            XCTAssertEqual(tokenValue, extractedToken)
+        } catch {
+            XCTFail("Preinstall error: \(error)")
+        }
+    }
+}