diff --git a/FirebaseAuth/Sources/Backend/FIRAuthBackend.h b/FirebaseAuth/Sources/Backend/FIRAuthBackend.h
index 452532a1b04..52dca974389 100644
--- a/FirebaseAuth/Sources/Backend/FIRAuthBackend.h
+++ b/FirebaseAuth/Sources/Backend/FIRAuthBackend.h
@@ -58,6 +58,8 @@
 @class FIRRevokeTokenResponse;
 @class FIRGetRecaptchaConfigRequest;
 @class FIRGetRecaptchaConfigResponse;
+@class FIRStartPasskeyEnrollmentRequest;
+@class FIRStartPasskeyEnrollmentResponse;
 
 @protocol FIRAuthBackendImplementation;
 @protocol FIRAuthBackendRPCIssuer;
@@ -243,15 +245,27 @@ typedef void (^FIRRevokeTokenResponseCallback)(FIRRevokeTokenResponse *_Nullable
 typedef void (^FIRSignInWithGameCenterResponseCallback)(
     FIRSignInWithGameCenterResponse *_Nullable response, NSError *_Nullable error);
 
-/** @typedef FIRGetRecaptchaConfigResponseCallback
-    @brief The type of block used to return the result of a call to the getRecaptchaConfig endpoint.
-    @param response The received response, if any.
-    @param error The error which occurred, if any.
-    @remarks One of response or error will be non-nil.
- */
+/**
+ @typedef FIRGetRecaptchaConfigResponseCallback
+ @brief The type of block used to return the result of a call to the getRecaptchaConfig endpoint.
+ @param response The received response, if any.
+ @param error The error which occurred, if any.
+ @remarks One of response or error will be non-nil.
+*/
 typedef void (^FIRGetRecaptchaConfigResponseCallback)(
     FIRGetRecaptchaConfigResponse *_Nullable response, NSError *_Nullable error);
 
+/**
+ @typedef FIRStartPasskeyEnrollmentResponseCallback
+ @brief The type of block used to return the result of a call to the StartPasskeyEnrollment
+endpoint.
+ @param response The received response, if any.
+ @param error The error which occurred, if any.
+ @remarks One of response or error will be non-nil.
+ */
+typedef void (^FIRStartPasskeyEnrollmentResponseCallback)(
+    FIRStartPasskeyEnrollmentResponse *_Nullable response, NSError *_Nullable error);
+
 /** @class FIRAuthBackend
     @brief Simple static class with methods representing the backend RPCs.
     @remarks All callback blocks passed as method parameters are invoked asynchronously on the
@@ -448,6 +462,17 @@ typedef void (^FIRGetRecaptchaConfigResponseCallback)(
 
 #endif
 
+#if TARGET_OS_IOS || TARGET_OS_TV || TARGET_OS_OSX || TARGET_OS_MACCATALYST
+/** @fn startPasskeyEnrollment:callback:
+    @brief Calls the startPasskeyEnrollment endpoint, which is responsible for receving the
+   challenge that will later be consumed for platform key creation.
+    @param request The request parameters.
+    @param callback The callback.
+ */
++ (void)startPasskeyEnrollment:(FIRStartPasskeyEnrollmentRequest *)request
+                      callback:(FIRStartPasskeyEnrollmentResponseCallback)callback;
+#endif
+
 /** @fn revokeToken:callback:
     @brief Calls the revokeToken endpoint, which is responsible for revoking the given token
         provided in the request parameters.
@@ -622,6 +647,17 @@ typedef void (^FIRGetRecaptchaConfigResponseCallback)(
 
 #endif
 
+#if TARGET_OS_IOS || TARGET_OS_TV || TARGET_OS_OSX || TARGET_OS_MACCATALYST
+/** @fn startPasskeyEnrollment:callback:
+    @brief Calls the startPasskeyEnrollment endpoint, which is responsible for receving the
+   challenge that will later be consumed for platform key creation.
+    @param request The request parameters.
+    @param callback The callback.
+ */
+- (void)startPasskeyEnrollment:(FIRStartPasskeyEnrollmentRequest *)request
+                      callback:(FIRStartPasskeyEnrollmentResponseCallback)callback;
+#endif
+
 /** @fn revokeToken:callback:
     @brief Calls the revokeToken endpoint, which is responsible for revoking the given token
         provided in the request parameters.
diff --git a/FirebaseAuth/Sources/Backend/FIRAuthBackend.m b/FirebaseAuth/Sources/Backend/FIRAuthBackend.m
index 6588611cc1a..53c98e00c0a 100644
--- a/FirebaseAuth/Sources/Backend/FIRAuthBackend.m
+++ b/FirebaseAuth/Sources/Backend/FIRAuthBackend.m
@@ -58,6 +58,8 @@
 #import "FirebaseAuth/Sources/Backend/RPC/FIRSignInWithGameCenterResponse.h"
 #import "FirebaseAuth/Sources/Backend/RPC/FIRSignUpNewUserRequest.h"
 #import "FirebaseAuth/Sources/Backend/RPC/FIRSignUpNewUserResponse.h"
+#import "FirebaseAuth/Sources/Backend/RPC/FIRStartPasskeyEnrollmentRequest.h"
+#import "FirebaseAuth/Sources/Backend/RPC/FIRStartPasskeyEnrollmentResponse.h"
 #import "FirebaseAuth/Sources/Backend/RPC/FIRVerifyAssertionRequest.h"
 #import "FirebaseAuth/Sources/Backend/RPC/FIRVerifyAssertionResponse.h"
 #import "FirebaseAuth/Sources/Backend/RPC/FIRVerifyClientRequest.h"
@@ -673,6 +675,13 @@ + (void)verifyClient:(id)request callback:(FIRVerifyClientResponseCallback)callb
 
 #endif
 
+#if TARGET_OS_IOS || TARGET_OS_TV || TARGET_OS_OSX || TARGET_OS_MACCATALYST
++ (void)startPasskeyEnrollment:(FIRStartPasskeyEnrollmentRequest *)request
+                      callback:(FIRStartPasskeyEnrollmentResponseCallback)callback {
+  [[self implementation] startPasskeyEnrollment:request callback:callback];
+}
+#endif
+
 + (void)revokeToken:(FIRRevokeTokenRequest *)request
            callback:(FIRRevokeTokenResponseCallback)callback {
   [[self implementation] revokeToken:request callback:callback];
@@ -1099,6 +1108,22 @@ - (void)verifyClient:(id)request callback:(FIRVerifyClientResponseCallback)callb
 
 #endif
 
+#if TARGET_OS_IOS || TARGET_OS_TV || TARGET_OS_OSX || TARGET_OS_MACCATALYST
+- (void)startPasskeyEnrollment:(FIRStartPasskeyEnrollmentRequest *)request
+                      callback:(FIRStartPasskeyEnrollmentResponseCallback)callback {
+  FIRStartPasskeyEnrollmentResponse *response = [[FIRStartPasskeyEnrollmentResponse alloc] init];
+  [self callWithRequest:request
+               response:response
+               callback:^(NSError *error) {
+                 if (error) {
+                   callback(nil, error);
+                   return;
+                 }
+                 callback(response, nil);
+               }];
+}
+#endif
+
 - (void)revokeToken:(FIRRevokeTokenRequest *)request
            callback:(FIRRevokeTokenResponseCallback)callback {
   FIRRevokeTokenResponse *response = [[FIRRevokeTokenResponse alloc] init];
diff --git a/FirebaseAuth/Sources/Backend/RPC/FIRStartPasskeyEnrollmentRequest.h b/FirebaseAuth/Sources/Backend/RPC/FIRStartPasskeyEnrollmentRequest.h
new file mode 100644
index 00000000000..75312439ec6
--- /dev/null
+++ b/FirebaseAuth/Sources/Backend/RPC/FIRStartPasskeyEnrollmentRequest.h
@@ -0,0 +1,38 @@
+/*
+ * Copyright 2023 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.
+ */
+
+#import "FirebaseAuth/Sources/Backend/FIRAuthRPCRequest.h"
+#import "FirebaseAuth/Sources/Backend/FIRIdentityToolkitRequest.h"
+
+NS_ASSUME_NONNULL_BEGIN
+
+/** @class FIRStartPasskeyEnrollmentRequest
+    @brief Represents the parameters for the startPasskeyEnrollment endpoint.
+ */
+@interface FIRStartPasskeyEnrollmentRequest : FIRIdentityToolkitRequest <FIRAuthRPCRequest>
+
+/**
+ @property IDToken
+ @brief The raw user access token
+ */
+@property(nonatomic, copy, readonly) NSString *IDToken;
+
+- (nullable instancetype)initWithIDToken:(NSString *)IDToken
+                    requestConfiguration:(FIRAuthRequestConfiguration *)requestConfiguration;
+
+@end
+
+NS_ASSUME_NONNULL_END
diff --git a/FirebaseAuth/Sources/Backend/RPC/FIRStartPasskeyEnrollmentRequest.m b/FirebaseAuth/Sources/Backend/RPC/FIRStartPasskeyEnrollmentRequest.m
new file mode 100644
index 00000000000..17051fcb639
--- /dev/null
+++ b/FirebaseAuth/Sources/Backend/RPC/FIRStartPasskeyEnrollmentRequest.m
@@ -0,0 +1,67 @@
+/*
+ * Copyright 2023 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.
+ */
+
+#import "FirebaseAuth/Sources/Backend/RPC/FIRStartPasskeyEnrollmentRequest.h"
+
+NS_ASSUME_NONNULL_BEGIN
+
+/**
+ @var kStartPasskeyEnrollmentEndPoint
+ @brief GCIP endpoint for startPasskeyEnrollment rpc
+ */
+static NSString *const kStartPasskeyEnrollmentEndPoint = @"accounts/passkeyEnrollment:start";
+
+/**
+ @var kTenantIDKey
+ @brief The key for the tenant id value in the request.
+ */
+static NSString *const kTenantIDKey = @"tenantId";
+
+/**
+ @var kIDToken
+ @brief The key for idToken value in the request.
+ */
+static NSString *const kIDToken = @"idToken";
+
+@implementation FIRStartPasskeyEnrollmentRequest
+
+- (nullable instancetype)initWithIDToken:(NSString *)IDToken
+                    requestConfiguration:(FIRAuthRequestConfiguration *)requestConfiguration {
+  self = [super initWithEndpoint:kStartPasskeyEnrollmentEndPoint
+            requestConfiguration:requestConfiguration];
+
+  if (self) {
+    _IDToken = IDToken;
+    self.useIdentityPlatform = YES;
+  }
+
+  return self;
+}
+
+- (nullable id)unencodedHTTPRequestBodyWithError:(NSError *__autoreleasing _Nullable *)error {
+  NSMutableDictionary *postBody = [NSMutableDictionary dictionary];
+  if (_IDToken) {
+    postBody[kIDToken] = _IDToken;
+  }
+  if (self.tenantID) {
+    postBody[kTenantIDKey] = self.tenantID;
+  }
+  return [postBody copy];
+}
+
+@end
+
+NS_ASSUME_NONNULL_END
diff --git a/FirebaseAuth/Sources/Backend/RPC/FIRStartPasskeyEnrollmentResponse.h b/FirebaseAuth/Sources/Backend/RPC/FIRStartPasskeyEnrollmentResponse.h
new file mode 100644
index 00000000000..ddd010a675b
--- /dev/null
+++ b/FirebaseAuth/Sources/Backend/RPC/FIRStartPasskeyEnrollmentResponse.h
@@ -0,0 +1,47 @@
+/*
+ * Copyright 2023 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.
+ */
+
+#import "FirebaseAuth/Sources/Backend/FIRAuthRPCResponse.h"
+
+NS_ASSUME_NONNULL_BEGIN
+
+/**
+ @class FIRStartPasskeyEnrollmentResponse
+ @brief Represents the response from the startPasskeyEnrollment endpoint.
+ */
+@interface FIRStartPasskeyEnrollmentResponse : NSObject <FIRAuthRPCResponse>
+
+/**
+ @property rpID
+ @brief The RP ID of the FIDO Relying Party.
+ */
+@property(nonatomic, readonly, copy) NSString *rpID;
+
+/**
+ @property userID
+ @brief The user ID.
+ */
+@property(nonatomic, readonly, copy) NSString *userID;
+
+/**
+ @property challenge
+ @brief The FIDO challenge.
+ */
+@property(nonatomic, readonly, copy) NSString *challenge;
+
+@end
+
+NS_ASSUME_NONNULL_END
diff --git a/FirebaseAuth/Sources/Backend/RPC/FIRStartPasskeyEnrollmentResponse.m b/FirebaseAuth/Sources/Backend/RPC/FIRStartPasskeyEnrollmentResponse.m
new file mode 100644
index 00000000000..aed8975f7bc
--- /dev/null
+++ b/FirebaseAuth/Sources/Backend/RPC/FIRStartPasskeyEnrollmentResponse.m
@@ -0,0 +1,75 @@
+/*
+ * Copyright 2023 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.
+ */
+
+#import "FirebaseAuth/Sources/Backend/RPC/FIRStartPasskeyEnrollmentResponse.h"
+
+/**
+ @var kOptionsKey
+ @brief The name of the field in the response JSON for CredentialCreationOptions.
+ */
+static const NSString *kOptionsKey = @"credentialCreationOptions";
+
+/**
+ @var kRpKey
+ @brief The name of the field in the response JSON for Relying Party.
+ */
+static const NSString *kRpKey = @"rp";
+
+/**
+ @var kUserKey
+ @brief The name of the field in the response JSON for User.
+ */
+static const NSString *kUserKey = @"user";
+
+/**
+ @var kIDKey
+ @brief The name of the field in the response JSON for ids.
+ */
+static const NSString *kIDKey = @"id";
+
+/**
+ @var kChallengeKey
+ @brief The name of the field in the response JSON for challenge.
+ */
+static const NSString *kChallengeKey = @"challenge";
+
+@implementation FIRStartPasskeyEnrollmentResponse
+
+- (BOOL)setWithDictionary:(nonnull NSDictionary *)dictionary
+                    error:(NSError *__autoreleasing _Nullable *_Nullable)error {
+  if (dictionary[kOptionsKey] == nil) {
+    return NO;
+  }
+  if (dictionary[kOptionsKey][kRpKey] == nil || dictionary[kOptionsKey][kRpKey][kIDKey] == nil) {
+    return NO;
+  }
+
+  if (dictionary[kOptionsKey][kUserKey] == nil ||
+      dictionary[kOptionsKey][kUserKey][kIDKey] == nil) {
+    return NO;
+  }
+
+  if (dictionary[kOptionsKey][kChallengeKey] == nil) {
+    return NO;
+  }
+
+  _rpID = dictionary[kOptionsKey][kRpKey][kIDKey];
+  _userID = dictionary[kOptionsKey][kUserKey][kIDKey];
+  _challenge = dictionary[kOptionsKey][kChallengeKey];
+  return YES;
+}
+
+@end
diff --git a/FirebaseAuth/Tests/Unit/FIRStartPasskeyEnrollmentRequestTests.m b/FirebaseAuth/Tests/Unit/FIRStartPasskeyEnrollmentRequestTests.m
new file mode 100644
index 00000000000..c31433a25e8
--- /dev/null
+++ b/FirebaseAuth/Tests/Unit/FIRStartPasskeyEnrollmentRequestTests.m
@@ -0,0 +1,104 @@
+/*
+ * Copyright 2023 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 <TargetConditionals.h>
+#if TARGET_OS_IOS || TARGET_OS_TV || TARGET_OS_OSX || TARGET_OS_MACCATALYST
+
+#import <XCTest/XCTest.h>
+
+#import "FirebaseAuth/Sources/Backend/RPC/FIRStartPasskeyEnrollmentRequest.h"
+#import "FirebaseAuth/Sources/Backend/RPC/FIRStartPasskeyEnrollmentResponse.h"
+#import "FirebaseAuth/Sources/Public/FirebaseAuth/FIRAuthErrors.h"
+#import "FirebaseAuth/Tests/Unit/FIRFakeBackendRPCIssuer.h"
+
+/**
+ @var kTestAPIKey
+ @brief Fake API key used for testing.
+ */
+static NSString *const kTestAPIKey = @"APIKey";
+
+/**
+ @var kTestFirebaseAppID
+ @brief Fake Firebase app ID used for testing.
+ */
+static NSString *const kTestFirebaseAppID = @"appID";
+
+/**
+ @var kExpectedAPIURL
+ @brief The expected URL for the test calls.
+ */
+static NSString *const kExpectedAPIURL =
+    @"https://identitytoolkit.googleapis.com/v2/accounts/passkeyEnrollment:start?key=APIKey";
+
+/**
+ @var kIDToken
+ @brief Token representing the user's identity.
+ */
+static NSString *const kIDToken = @"idToken";
+
+/**
+ @class FIRStartPasskeyEnrollmentRequestTests
+ @brief Tests for @c FIRStartPasskeyEnrollmentRequest.
+ */
+@interface FIRStartPasskeyEnrollmentRequestTests : XCTestCase
+@end
+
+@implementation FIRStartPasskeyEnrollmentRequestTests {
+  /**
+   @brief This backend RPC issuer is used to fake network responses for each test in the suite.
+   In the @c setUp method we initialize this and set @c FIRAuthBackend's RPC issuer to it.
+   */
+  FIRFakeBackendRPCIssuer *_RPCIssuer;
+
+  /**
+   @brief This is the request configuration used for testing.
+   */
+  FIRAuthRequestConfiguration *_requestConfiguration;
+}
+
+- (void)setUp {
+  [super setUp];
+  FIRFakeBackendRPCIssuer *RPCIssuer = [[FIRFakeBackendRPCIssuer alloc] init];
+  [FIRAuthBackend setDefaultBackendImplementationWithRPCIssuer:RPCIssuer];
+  _RPCIssuer = RPCIssuer;
+  _requestConfiguration = [[FIRAuthRequestConfiguration alloc] initWithAPIKey:kTestAPIKey
+                                                                        appID:kTestFirebaseAppID];
+}
+
+- (void)tearDown {
+  _RPCIssuer = nil;
+  _requestConfiguration = nil;
+  [FIRAuthBackend setDefaultBackendImplementationWithRPCIssuer:nil];
+  [super tearDown];
+}
+
+- (void)testStartPasskeyEnrollmentRequest {
+  FIRStartPasskeyEnrollmentRequest *request =
+      [[FIRStartPasskeyEnrollmentRequest alloc] initWithIDToken:kIDToken
+                                           requestConfiguration:_requestConfiguration];
+
+  [FIRAuthBackend startPasskeyEnrollment:request
+                                callback:^(FIRStartPasskeyEnrollmentResponse *_Nullable response,
+                                           NSError *_Nullable error){
+                                }];
+
+  XCTAssertEqualObjects(_RPCIssuer.requestURL.absoluteString, kExpectedAPIURL);
+  XCTAssertNotNil(_RPCIssuer.decodedRequest);
+  XCTAssertEqualObjects(_RPCIssuer.decodedRequest[kIDToken], kIDToken);
+}
+
+@end
+#endif
diff --git a/FirebaseAuth/Tests/Unit/FIRStartPasskeyEnrollmentResponseTests.m b/FirebaseAuth/Tests/Unit/FIRStartPasskeyEnrollmentResponseTests.m
new file mode 100644
index 00000000000..ca3286d3b1c
--- /dev/null
+++ b/FirebaseAuth/Tests/Unit/FIRStartPasskeyEnrollmentResponseTests.m
@@ -0,0 +1,311 @@
+/*
+ * Copyright 2023 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 <XCTest/XCTest.h>
+
+#if TARGET_OS_IOS || TARGET_OS_TV || TARGET_OS_OSX || TARGET_OS_MACCATALYST
+#import "FirebaseAuth/Sources/Public/FirebaseAuth/FIRAuthErrors.h"
+
+#import "FirebaseAuth/Sources/Backend/FIRAuthBackend.h"
+#import "FirebaseAuth/Sources/Backend/RPC/FIRStartPasskeyEnrollmentRequest.h"
+#import "FirebaseAuth/Sources/Backend/RPC/FIRStartPasskeyEnrollmentResponse.h"
+#import "FirebaseAuth/Sources/Utilities/FIRAuthInternalErrors.h"
+#import "FirebaseAuth/Tests/Unit/FIRFakeBackendRPCIssuer.h"
+
+/**
+ @var kTestAPIKey
+ @brief Fake API key used for testing.
+ */
+static NSString *const kTestAPIKey = @"APIKey";
+
+/**
+ @var kTestFirebaseAppID
+ @brief Fake Firebase app ID used for testing.
+ */
+static NSString *const kTestFirebaseAppID = @"appID";
+
+/**
+ @var kIDToken
+ @brief Token representing the user's identity.
+ */
+static NSString *const kIDToken = @"idToken";
+
+/**
+ @var kTestRpID
+ @brief Fake Relying Party ID used for testing.
+ */
+static NSString *const kTestRpID = @"1234567890";
+
+/**
+ @var kTestChallenge
+ @brief Fake challenge used for testing.
+ */
+static NSString *const kTestChallenge = @"challengebytes";
+
+/**
+ @var kTestUserID
+ @brief Fake user id used for testing.
+ */
+static NSString *const kTestUserID = @"user-id";
+
+/**
+ @var kUsersKey
+ @brief the name of the "users" property in the response.
+ */
+static NSString *const kUsersKey = @"users";
+
+/**
+ @var kTestRpKey
+ @brief the name of the "rp" property in the response.
+ */
+static NSString *const kTestRpKey = @"rp";
+
+/**
+ @var kTestChallengeKey
+ @brief the name of the "challenge" property in the response.
+ */
+static NSString *const kTestChallengeKey = @"challenge";
+
+/**
+ @var kTestUserKey
+ @brief the name of the "user" property in the response.
+ */
+static NSString *const kTestUserKey = @"user";
+
+/**
+ @var kTestIDKey
+ @brief the name of the "id" property in the response.
+ */
+static NSString *const kTestIDKey = @"id";
+
+/**
+ @class FIRStartPasskeyEnrollmentResponseTests
+ @brief Tests for @c FIRStartPasskeyEnrollmentResponse.
+ */
+@interface FIRStartPasskeyEnrollmentResponseTests : XCTestCase
+@end
+@implementation FIRStartPasskeyEnrollmentResponseTests {
+  /**
+   @brief This backend RPC issuer is used to fake network responses for each test in the suite.
+   In the @c setUp method we initialize this and set @c FIRAuthBackend's RPC issuer to it.
+   */
+  FIRFakeBackendRPCIssuer *_RPCIssuer;
+
+  /**
+   @brief This is the request configuration used for testing.
+   */
+  FIRAuthRequestConfiguration *_requestConfiguration;
+}
+
+- (void)setUp {
+  [super setUp];
+  FIRFakeBackendRPCIssuer *RPCIssuer = [[FIRFakeBackendRPCIssuer alloc] init];
+  [FIRAuthBackend setDefaultBackendImplementationWithRPCIssuer:RPCIssuer];
+  _RPCIssuer = RPCIssuer;
+  _requestConfiguration = [[FIRAuthRequestConfiguration alloc] initWithAPIKey:kTestAPIKey
+                                                                        appID:kTestFirebaseAppID];
+}
+
+- (void)tearDown {
+  _RPCIssuer = nil;
+  _requestConfiguration = nil;
+  [FIRAuthBackend setDefaultBackendImplementationWithRPCIssuer:nil];
+  [super tearDown];
+}
+
+/** @fn testSuccessfulStartPasskeyEnrollmentResponse
+    @brief This test simulates a successful @c StartPasskeyEnrollment flow.
+ */
+- (void)testSuccessfulStartPasskeyEnrollmentResponse {
+  FIRStartPasskeyEnrollmentRequest *request =
+      [[FIRStartPasskeyEnrollmentRequest alloc] initWithIDToken:kIDToken
+                                           requestConfiguration:_requestConfiguration];
+
+  __block BOOL callbackInvoked;
+  __block FIRStartPasskeyEnrollmentResponse *RPCResponse;
+  __block NSError *RPCError;
+
+  [FIRAuthBackend startPasskeyEnrollment:request
+                                callback:^(FIRStartPasskeyEnrollmentResponse *_Nullable response,
+                                           NSError *_Nullable error) {
+                                  callbackInvoked = YES;
+                                  RPCResponse = response;
+                                  RPCError = error;
+                                }];
+
+  [_RPCIssuer respondWithJSON:@{
+    @"credentialCreationOptions" : @{
+      kTestChallengeKey : kTestChallenge,
+      kTestRpKey : @{kTestIDKey : kTestRpID},
+      kTestUserKey : @{kTestIDKey : kTestUserID},
+    },
+  }];
+
+  XCTAssert(callbackInvoked);
+  XCTAssertNil(RPCError);
+  XCTAssertNotNil(RPCResponse);
+  XCTAssertEqualObjects(RPCResponse.rpID, kTestRpID);
+  XCTAssertEqualObjects(RPCResponse.challenge, kTestChallenge);
+  XCTAssertEqualObjects(RPCResponse.userID, kTestUserID);
+}
+
+/** @fn testStartPasskeyEnrollmentResponseMissingCreationOptionsError
+    @brief This test simulates an unexpected response returned from server in @c
+   StartPasskeyEnrollment flow.
+ */
+- (void)testStartPasskeyEnrollmentResponseMissingCreationOptionsError {
+  FIRStartPasskeyEnrollmentRequest *request =
+      [[FIRStartPasskeyEnrollmentRequest alloc] initWithIDToken:kIDToken
+                                           requestConfiguration:_requestConfiguration];
+
+  __block BOOL callbackInvoked;
+  __block FIRStartPasskeyEnrollmentResponse *RPCResponse;
+  __block NSError *RPCError;
+
+  [FIRAuthBackend startPasskeyEnrollment:request
+                                callback:^(FIRStartPasskeyEnrollmentResponse *_Nullable response,
+                                           NSError *_Nullable error) {
+                                  callbackInvoked = YES;
+                                  RPCResponse = response;
+                                  RPCError = error;
+                                }];
+
+  [_RPCIssuer respondWithJSON:@{
+    @"wrongkey" : @{},
+  }];
+  [self errorValidationHelperWithCallbackInvoked:callbackInvoked
+                                        rpcError:RPCError
+                                     rpcResponse:RPCResponse];
+}
+
+/** @fn testStartPasskeyEnrollmentResponseMissingRpIdError
+    @brief This test simulates an unexpected response returned from server in @c
+   StartPasskeyEnrollment flow.
+ */
+- (void)testStartPasskeyEnrollmentResponseMissingRpIdError {
+  FIRStartPasskeyEnrollmentRequest *request =
+      [[FIRStartPasskeyEnrollmentRequest alloc] initWithIDToken:kIDToken
+                                           requestConfiguration:_requestConfiguration];
+
+  __block BOOL callbackInvoked;
+  __block FIRStartPasskeyEnrollmentResponse *RPCResponse;
+  __block NSError *RPCError;
+
+  [FIRAuthBackend startPasskeyEnrollment:request
+                                callback:^(FIRStartPasskeyEnrollmentResponse *_Nullable response,
+                                           NSError *_Nullable error) {
+                                  callbackInvoked = YES;
+                                  RPCResponse = response;
+                                  RPCError = error;
+                                }];
+
+  [_RPCIssuer respondWithJSON:@{
+    @"credentialCreationOptions" : @{
+      kTestChallengeKey : kTestChallenge,
+      kTestRpKey : @{},
+      kTestUserKey : @{kTestIDKey : kTestUserID},
+    },
+  }];
+  [self errorValidationHelperWithCallbackInvoked:callbackInvoked
+                                        rpcError:RPCError
+                                     rpcResponse:RPCResponse];
+}
+
+/** @fn testStartPasskeyEnrollmentResponseMissingUserIdError
+    @brief This test simulates an unexpected response returned from server in @c
+   StartPasskeyEnrollment flow.
+ */
+- (void)testStartPasskeyEnrollmentResponseMissingUserIdError {
+  FIRStartPasskeyEnrollmentRequest *request =
+      [[FIRStartPasskeyEnrollmentRequest alloc] initWithIDToken:kIDToken
+                                           requestConfiguration:_requestConfiguration];
+
+  __block BOOL callbackInvoked;
+  __block FIRStartPasskeyEnrollmentResponse *RPCResponse;
+  __block NSError *RPCError;
+
+  [FIRAuthBackend startPasskeyEnrollment:request
+                                callback:^(FIRStartPasskeyEnrollmentResponse *_Nullable response,
+                                           NSError *_Nullable error) {
+                                  callbackInvoked = YES;
+                                  RPCResponse = response;
+                                  RPCError = error;
+                                }];
+
+  [_RPCIssuer respondWithJSON:@{
+    @"credentialCreationOptions" : @{
+      kTestChallengeKey : kTestChallenge,
+      kTestRpKey : @{kTestIDKey : kTestRpID},
+      kTestUserKey : @{},
+    },
+  }];
+  [self errorValidationHelperWithCallbackInvoked:callbackInvoked
+                                        rpcError:RPCError
+                                     rpcResponse:RPCResponse];
+}
+
+/** @fn testStartPasskeyEnrollmentResponseMissingChallengeError
+    @brief This test simulates an unexpected response returned from server in @c
+   StartPasskeyEnrollment flow.
+ */
+- (void)testStartPasskeyEnrollmentResponseMissingChallengeError {
+  FIRStartPasskeyEnrollmentRequest *request =
+      [[FIRStartPasskeyEnrollmentRequest alloc] initWithIDToken:kIDToken
+                                           requestConfiguration:_requestConfiguration];
+
+  __block BOOL callbackInvoked;
+  __block FIRStartPasskeyEnrollmentResponse *RPCResponse;
+  __block NSError *RPCError;
+
+  [FIRAuthBackend startPasskeyEnrollment:request
+                                callback:^(FIRStartPasskeyEnrollmentResponse *_Nullable response,
+                                           NSError *_Nullable error) {
+                                  callbackInvoked = YES;
+                                  RPCResponse = response;
+                                  RPCError = error;
+                                }];
+
+  [_RPCIssuer respondWithJSON:@{
+    @"credentialCreationOptions" : @{
+      kTestRpKey : @{kTestIDKey : kTestRpID},
+      kTestUserKey : @{kTestIDKey : kTestUserID},
+    },
+  }];
+  [self errorValidationHelperWithCallbackInvoked:callbackInvoked
+                                        rpcError:RPCError
+                                     rpcResponse:RPCResponse];
+}
+
+/** @fn errorValidationHelperWithCallbackInvoked:rpcError:rpcResponse:
+    @brief Helper function to validate the unexpected response returned from server in @c
+   StartPasskeyEnrollment flow.
+ */
+- (void)errorValidationHelperWithCallbackInvoked:(BOOL)callbackInvoked
+                                        rpcError:(NSError *)RPCError
+                                     rpcResponse:(FIRStartPasskeyEnrollmentResponse *)RPCResponse {
+  XCTAssert(callbackInvoked);
+  XCTAssertNotNil(RPCError);
+  XCTAssertEqualObjects(RPCError.domain, FIRAuthErrorDomain);
+  XCTAssertEqual(RPCError.code, FIRAuthErrorCodeInternalError);
+  XCTAssertNotNil(RPCError.userInfo[NSUnderlyingErrorKey]);
+  NSError *underlyingError = RPCError.userInfo[NSUnderlyingErrorKey];
+  XCTAssertNotNil(underlyingError);
+  XCTAssertNotNil(underlyingError.userInfo[FIRAuthErrorUserInfoDeserializedResponseKey]);
+  XCTAssertNil(RPCResponse);
+}
+
+@end
+#endif