implementing start passkey sign-in (#15168)

Author: srushtisv

FirebaseAuth/Sources/Swift/Auth/Auth.swift

@@ -29,6 +29,10 @@ import FirebaseCoreExtension
   import UIKit
 #endif
 
+#if os(iOS) || os(tvOS) || os(macOS) || targetEnvironment(macCatalyst)
+  import AuthenticationServices
+#endif
+
 // Export the deprecated Objective-C defined globals and typedefs.
 #if SWIFT_PACKAGE
   @_exported import FirebaseAuthInternal
@@ -1641,6 +1645,60 @@ extension Auth: AuthInterop {
   public static let authStateDidChangeNotification =
     NSNotification.Name(rawValue: "FIRAuthStateDidChangeNotification")
 
+  // MARK: Passkey Implementation
+
+  #if os(iOS) || os(tvOS) || os(macOS) || targetEnvironment(macCatalyst)
+
+    /// starts sign in with passkey retrieving challenge from GCIP and create an assertion request.
+    @available(iOS 15.0, macOS 12.0, tvOS 16.0, *)
+    public func startPasskeySignIn() async throws ->
+      ASAuthorizationPlatformPublicKeyCredentialAssertionRequest {
+      let request = StartPasskeySignInRequest(requestConfiguration: requestConfiguration)
+      let response = try await backend.call(with: request)
+      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."]
+        )
+      }
+      let provider = ASAuthorizationPlatformPublicKeyCredentialProvider(
+        relyingPartyIdentifier: response.rpID
+      )
+      return provider.createCredentialAssertionRequest(
+        challenge: challengeInData
+      )
+    }
+
+    ///  finalize sign in with passkey with existing credential assertion.
+    ///  - Parameter platformCredential The existing credential  assertion created by device.
+    @available(iOS 15.0, macOS 12.0, tvOS 16.0, *)
+    public func finalizePasskeySignIn(withPlatformCredential platformCredential: ASAuthorizationPlatformPublicKeyCredentialAssertion) async throws
+      -> AuthDataResult {
+      let credentialID = platformCredential.credentialID.base64EncodedString()
+      let clientDataJSON = platformCredential.rawClientDataJSON.base64EncodedString()
+      let authenticatorData = platformCredential.rawAuthenticatorData.base64EncodedString()
+      let signature = platformCredential.signature.base64EncodedString()
+      let userID = platformCredential.userID.base64EncodedString()
+      let request = FinalizePasskeySignInRequest(
+        credentialID: credentialID,
+        clientDataJSON: clientDataJSON,
+        authenticatorData: authenticatorData,
+        signature: signature,
+        userId: userID,
+        requestConfiguration: requestConfiguration
+      )
+      let response = try await backend.call(with: request)
+      let user = try await Auth.auth().completeSignIn(
+        withAccessToken: response.idToken,
+        accessTokenExpirationDate: nil,
+        refreshToken: response.refreshToken,
+        anonymous: false
+      )
+      return AuthDataResult(withUser: user, additionalUserInfo: nil)
+    }
+  #endif
+
   // MARK: Internal methods
 
   init(app: FirebaseApp,

FirebaseAuth/Sources/Swift/Backend/AuthBackend.swift

@@ -440,6 +440,7 @@ final class AuthBackend: AuthBackendProtocol {
       return AuthErrorUtils.credentialAlreadyInUseError(
         message: serverDetailErrorMessage, credential: credential, email: email
       )
+    case "INVALID_AUTHENTICATOR_RESPONSE": return AuthErrorUtils.invalidAuthenticatorResponse()
     default:
       if let underlyingErrors = errorDictionary["errors"] as? [[String: String]] {
         for underlyingError in underlyingErrors {

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

@@ -0,0 +1,68 @@
+/*
+ * 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/LICENSE2.0
+ *
+ * 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.
+ */
+
+/// The GCIP endpoint for finalizePasskeySignIn rpc
+private let finalizePasskeySignInEndPoint = "accounts/passkeySignIn:finalize"
+
+class FinalizePasskeySignInRequest: IdentityToolkitRequest, AuthRPCRequest {
+  typealias Response = FinalizePasskeySignInResponse
+  /// The credential ID
+  let credentialID: String
+  /// The CollectedClientData object from the authenticator.
+  let clientDataJSON: String
+  /// The AuthenticatorData from the authenticator.
+  let authenticatorData: String
+  ///  The signature from the authenticator.
+  let signature: String
+  /// The user handle
+  let userId: String
+
+  init(credentialID: String,
+       clientDataJSON: String,
+       authenticatorData: String,
+       signature: String,
+       userId: String,
+       requestConfiguration: AuthRequestConfiguration) {
+    self.credentialID = credentialID
+    self.clientDataJSON = clientDataJSON
+    self.authenticatorData = authenticatorData
+    self.signature = signature
+    self.userId = userId
+    super.init(
+      endpoint: finalizePasskeySignInEndPoint,
+      requestConfiguration: requestConfiguration,
+      useIdentityPlatform: true
+    )
+  }
+
+  var unencodedHTTPRequestBody: [String: AnyHashable]? {
+    var postBody: [String: AnyHashable] = [
+      "authenticatorAssertionResponse": [
+        "credentialId": credentialID,
+        "authenticatorAssertionResponse": [
+          "clientDataJSON": clientDataJSON,
+          "authenticatorData": authenticatorData,
+          "signature": signature,
+          "userHandle": userId,
+        ],
+      ] as [String: AnyHashable],
+    ]
+    if let tenantID = tenantID {
+      postBody["tenantId"] = tenantID
+    }
+    return postBody
+  }
+}

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

@@ -0,0 +1,33 @@
+/*
+ * 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/LICENSE2.0
+ *
+ * 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.
+ */
+
+struct FinalizePasskeySignInResponse: AuthRPCResponse {
+  /// The user raw access token.
+  let idToken: String
+  /// Refresh token for the authenticated user.
+  let refreshToken: String
+
+  init(dictionary: [String: AnyHashable]) throws {
+    guard
+      let idToken = dictionary["idToken"] as? String,
+      let refreshToken = dictionary["refreshToken"] as? String
+    else {
+      throw AuthErrorUtils.unexpectedResponse(deserializedResponse: dictionary)
+    }
+    self.idToken = idToken
+    self.refreshToken = refreshToken
+  }
+}

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

@@ -0,0 +1,36 @@
+// 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.
+
+/// The GCIP endpoint for startPasskeySignIn rpc
+private let startPasskeySignInEndpoint = "accounts/passkeySignIn:start"
+
+@available(iOS 15.0, macOS 12.0, tvOS 16.0, *)
+class StartPasskeySignInRequest: IdentityToolkitRequest, AuthRPCRequest {
+  typealias Response = StartPasskeySignInResponse
+
+  init(requestConfiguration: AuthRequestConfiguration) {
+    super.init(
+      endpoint: startPasskeySignInEndpoint,
+      requestConfiguration: requestConfiguration,
+      useIdentityPlatform: true
+    )
+  }
+
+  var unencodedHTTPRequestBody: [String: AnyHashable]? {
+    guard let tenantID = tenantID else {
+      return nil
+    }
+    return ["tenantId": tenantID]
+  }
+}

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

@@ -0,0 +1,33 @@
+// 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.
+
+@available(iOS 15.0, macOS 12.0, tvOS 16.0, *)
+struct StartPasskeySignInResponse: AuthRPCResponse {
+  /// The RP ID of the FIDO Relying Party
+  let rpID: String
+  /// The FIDO challenge
+  let challenge: String
+
+  init(dictionary: [String: AnyHashable]) throws {
+    guard let options = dictionary["credentialRequestOptions"] as? [String: Any] else {
+      throw AuthErrorUtils.unexpectedResponse(deserializedResponse: dictionary)
+    }
+    guard let rpID = options["rpId"] as? String,
+          let challenge = options["challenge"] as? String else {
+      throw AuthErrorUtils.unexpectedResponse(deserializedResponse: dictionary)
+    }
+    self.rpID = rpID
+    self.challenge = challenge
+  }
+}

FirebaseAuth/Sources/Swift/Utilities/AuthErrorUtils.swift

@@ -207,6 +207,10 @@ class AuthErrorUtils {
     error(code: .invalidRecaptchaToken)
   }
 
+  static func invalidAuthenticatorResponse() -> Error {
+    error(code: .invalidAuthenticatorResponse)
+  }
+
   static func unauthorizedDomainError(message: String?) -> Error {
     error(code: .unauthorizedDomain, message: message)
   }

FirebaseAuth/Sources/Swift/Utilities/AuthErrors.swift

@@ -336,6 +336,10 @@ import Foundation
   /// Indicates that the reCAPTCHA SDK actions class failed to create.
   case recaptchaActionCreationFailed = 17210
 
+  /// the authenticator response for passkey signin or enrollment is not parseable, missing required
+  /// fields, or certain fields are invalid values
+  case invalidAuthenticatorResponse = 17211
+
   /// Indicates an error occurred while attempting to access the keychain.
   case keychainError = 17995
 
@@ -528,6 +532,8 @@ import Foundation
       return kErrorSiteKeyMissing
     case .recaptchaActionCreationFailed:
       return kErrorRecaptchaActionCreationFailed
+    case .invalidAuthenticatorResponse:
+      return kErrorInvalidAuthenticatorResponse
     }
   }
 
@@ -719,6 +725,8 @@ import Foundation
       return "ERROR_RECAPTCHA_SITE_KEY_MISSING"
     case .recaptchaActionCreationFailed:
       return "ERROR_RECAPTCHA_ACTION_CREATION_FAILED"
+    case .invalidAuthenticatorResponse:
+      return "ERROR_INVALID_AUTHENTICATOR_RESPONSE"
     }
   }
 }
@@ -996,3 +1004,6 @@ private let kErrorSiteKeyMissing =
 private let kErrorRecaptchaActionCreationFailed =
   "The reCAPTCHA SDK action class failed to initialize. See " +
   "https://cloud.google.com/recaptcha-enterprise/docs/instrument-ios-apps"
+
+private let kErrorInvalidAuthenticatorResponse =
+  "During passkey enrollment and sign in, the authenticator response is not parseable, missing required fields, or certain fields are invalid values that compromise the security of the sign-in or enrollment."