Rewrite AppCheckCore in Swift (#111)

Signed-off-by: Nick Cooke <36927374+ncooke3@users.noreply.github.com>
Co-authored-by: Nick Cooke <36927374+ncooke3@users.noreply.github.com>
Co-authored-by: Nick Cooke <nickcooke@google.com>

AppCheckCore/Sources/DebugProvider/AppCheckCoreDebugProviderAPIService.swift

@@ -0,0 +1,69 @@
+// Copyright 2026 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+import Foundation
+
+protocol AppCheckCoreDebugProviderAPIServiceProtocol: NSObjectProtocol {
+  func appCheckToken(debugToken: String, limitedUse: Bool) async throws -> AppCheckCoreToken
+}
+
+class AppCheckCoreDebugProviderAPIService: NSObject, AppCheckCoreDebugProviderAPIServiceProtocol {
+  private let apiService: AppCheckCoreAPIServiceProtocol
+  private let resourceName: String
+
+  private static let contentTypeKey = "Content-Type"
+  private static let jsonContentType = "application/json"
+  private static let debugTokenField = "debug_token"
+  private static let limitedUseField = "limited_use"
+
+  init(apiService: AppCheckCoreAPIServiceProtocol, resourceName: String) {
+    self.apiService = apiService
+    self.resourceName = resourceName
+    super.init()
+  }
+
+  func appCheckToken(debugToken: String, limitedUse: Bool) async throws -> AppCheckCoreToken {
+    let urlString = "\(apiService.baseURL)/\(resourceName):exchangeDebugToken"
+    guard let url = URL(string: urlString) else {
+      throw AppCheckCoreErrorUtil.error(withFailureReason: "Invalid URL: \(urlString)")
+    }
+
+    let httpBody = try self.httpBody(debugToken: debugToken, limitedUse: limitedUse)
+
+    let response = try await apiService.sendRequest(withURL: url,
+                                                    httpMethod: "POST",
+                                                    body: httpBody,
+                                                    additionalHeaders: [Self.contentTypeKey: Self
+                                                      .jsonContentType])
+
+    return try apiService.appCheckToken(withAPIResponse: response)
+  }
+
+  private func httpBody(debugToken: String, limitedUse: Bool) throws -> Data {
+    if debugToken.isEmpty {
+      throw AppCheckCoreErrorUtil.error(withFailureReason: "Debug token must not be empty.")
+    }
+
+    let payload: [String: Any] = [
+      Self.debugTokenField: debugToken,
+      Self.limitedUseField: limitedUse,
+    ]
+
+    do {
+      return try JSONSerialization.data(withJSONObject: payload, options: [])
+    } catch {
+      throw AppCheckCoreErrorUtil.jsonSerializationError(error)
+    }
+  }
+}