implement start passkey enrollment

Author: srushtisv

FirebaseAuth/Sources/Swift/Backend/RPC/StartPasskeyEnrollmentRequest.swift

@@ -0,0 +1,46 @@
+// Copyright 2025 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
+
+/// The GCIP endpoint for startPasskeyEnrollment rpc
+private let startPasskeyEnrollmentEndPoint = "accounts/passkeyEnrollment:start"
+
+@available(iOS 15.0, macOS 12.0, tvOS 16.0, *)
+class StartPasskeyEnrollmentRequest: IdentityToolkitRequest, AuthRPCRequest {
+  typealias Response = StartPasskeyEnrollmentResponse
+
+  /// The raw user access token
+  let idToken: String
+
+  init(idToken: String,
+       requestConfiguration: AuthRequestConfiguration) {
+    self.idToken = idToken
+    super.init(
+      endpoint: startPasskeyEnrollmentEndPoint,
+      requestConfiguration: requestConfiguration,
+      useIdentityPlatform: true
+    )
+  }
+
+  var unencodedHTTPRequestBody: [String: AnyHashable]? {
+    var body: [String: AnyHashable] = [
+      "idToken": idToken,
+    ]
+    if let tenantID = tenantID {
+      body["tenantId"] = tenantID
+    }
+    return body
+  }
+}

FirebaseAuth/Sources/Swift/Backend/RPC/StartPasskeyEnrollmentResponse.swift

@@ -0,0 +1,45 @@
+// Copyright 2025 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
+
+@available(iOS 15.0, macOS 12.0, tvOS 16.0, *)
+struct StartPasskeyEnrollmentResponse: AuthRPCResponse {
+  /// The RP ID of the FIDO Relying Party.
+  let rpID: String
+  /// The user id
+  let userID: String
+  /// The FIDO challenge.
+  let challenge: String
+
+  init(dictionary: [String: AnyHashable]) throws {
+    guard let options = dictionary["credentialCreationOptions"] as? [String: Any] else {
+      throw AuthErrorUtils.unexpectedResponse(deserializedResponse: dictionary)
+    }
+    guard let rp = options["rp"] as? [String: Any],
+          let rpID = rp["id"] as? String else {
+      throw AuthErrorUtils.unexpectedResponse(deserializedResponse: dictionary)
+    }
+    guard let user = options["user"] as? [String: Any],
+          let userID = user["id"] as? String else {
+      throw AuthErrorUtils.unexpectedResponse(deserializedResponse: dictionary)
+    }
+    guard let challenge = options["challenge"] as? String else {
+      throw AuthErrorUtils.unexpectedResponse(deserializedResponse: dictionary)
+    }
+    self.rpID = rpID
+    self.userID = userID
+    self.challenge = challenge
+  }
+}

FirebaseAuth/Sources/Swift/User/User.swift

@@ -14,6 +14,10 @@
 
 import Foundation
 
+#if os(iOS) || os(tvOS) || os(macOS) || targetEnvironment(macCatalyst)
+  import AuthenticationServices
+#endif
+
 @available(iOS 13, tvOS 13, macOS 10.15, macCatalyst 13, watchOS 7, *)
 extension User: NSSecureCoding {}
 
@@ -1047,6 +1051,59 @@ extension User: NSSecureCoding {}
     }
   }
 
+  // MARK: Passkey Implementation
+
+  #if os(iOS) || os(tvOS) || os(macOS) || targetEnvironment(macCatalyst)
+
+    /// A cached passkey name being passed from startPasskeyEnrollment(withName:) call and consumed
+    /// at finalizePasskeyEnrollment(withPlatformCredential:) call
+    private var passkeyName: String?
+
+    /// Start the passkey enrollment creating a plaform public key creation request with the
+    /// challenge from GCIP backend.
+    /// - Parameter name: The name for the passkey to be created.
+    @available(iOS 15.0, macOS 12.0, tvOS 16.0, *)
+    public func startPasskeyEnrollment(withName name: String?) async throws
+      -> ASAuthorizationPlatformPublicKeyCredentialRegistrationRequest {
+      guard auth != nil else {
+        /// If auth is nil, this User object is in an invalid state for this operation.
+        fatalError(
+          "Firebase Auth Internal Error: Set user's auth property with non-nil instance. Cannot start passkey enrollment."
+        )
+      }
+      let enrollmentIdToken = rawAccessToken()
+      let request = StartPasskeyEnrollmentRequest(
+        idToken: enrollmentIdToken,
+        requestConfiguration: requestConfiguration
+      )
+      let response = try await backend.call(with: request)
+      passkeyName = (name?.isEmpty ?? true) ? "Unnamed account (Apple)" : name!
+      guard let challengeInData = Data(base64Encoded: response.challenge) else {
+        throw NSError(
+          domain: AuthErrorDomain,
+          code: AuthInternalErrorCode.RPCResponseDecodingError.rawValue,
+          userInfo: [NSLocalizedDescriptionKey: "Failed to decode base64 challenge from response."]
+        )
+      }
+      guard let userIdInData = Data(base64Encoded: response.userID) else {
+        throw NSError(
+          domain: AuthErrorDomain,
+          code: AuthInternalErrorCode.RPCResponseDecodingError.rawValue,
+          userInfo: [NSLocalizedDescriptionKey: "Failed to decode base64 userId from response."]
+        )
+      }
+      let provider = ASAuthorizationPlatformPublicKeyCredentialProvider(
+        relyingPartyIdentifier: response.rpID
+      )
+      let registrationRequest = provider.createCredentialRegistrationRequest(
+        challenge: challengeInData,
+        name: passkeyName ?? "Unnamed account (Apple)",
+        userID: userIdInData
+      )
+      return registrationRequest
+    }
+  #endif
+
   // MARK: Internal implementations below
 
   func rawAccessToken() -> String {