diff --git a/FirebaseAuth/Sources/Backend/FIRAuthBackend.h b/FirebaseAuth/Sources/Backend/FIRAuthBackend.h
index 1a928888f38..a105bc3b5ee 100644
--- a/FirebaseAuth/Sources/Backend/FIRAuthBackend.h
+++ b/FirebaseAuth/Sources/Backend/FIRAuthBackend.h
@@ -64,6 +64,8 @@
 @class FIRFinalizePasskeyEnrollmentResponse;
 @class FIRStartPasskeySignInRequest;
 @class FIRStartPasskeySignInResponse;
+@class FIRFinalizePasskeySignInRequest;
+@class FIRFinalizePasskeySignInResponse;
 
 @protocol FIRAuthBackendImplementation;
 @protocol FIRAuthBackendRPCIssuer;
@@ -272,7 +274,7 @@ typedef void (^FIRStartPasskeyEnrollmentResponseCallback)(
 
 /**
  @typedef FIRFinalizePasskeyEnrollmentResponseCallback
- @brief The type of block used to return the result of a call to the startPasskeyEnrollment
+ @brief The type of block used to return the result of a call to the finalizePasskeyEnrollment
  endpoint.
  @param response The received response, if any.
  @param error The error which occurred, if any.
@@ -292,6 +294,17 @@ endpoint.
 typedef void (^FIRStartPasskeySignInResponseCallback)(
     FIRStartPasskeySignInResponse *_Nullable response, NSError *_Nullable error);
 
+/**
+ @typedef FIRFinalizePasskeySignInResponseCallback
+ @brief The type of block used to return the result of a call to the finalizePasskeySignIn
+ 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 (^FIRFinalizePasskeySignInResponseCallback)(
+    FIRFinalizePasskeySignInResponse *_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
@@ -514,6 +527,14 @@ typedef void (^FIRStartPasskeySignInResponseCallback)(
  */
 + (void)startPasskeySignIn:(FIRStartPasskeySignInRequest *)request
                   callback:(FIRStartPasskeySignInResponseCallback)callback;
+
+/** @fn finalizePasskeySignIn:callback:
+    @brief Sends the platform created public info to the finalizePasskeySignIn endpoint.
+    @param request The request parameters.
+    @param callback The callback.
+ */
++ (void)finalizePasskeySignIn:(FIRFinalizePasskeySignInRequest *)request
+                     callback:(FIRFinalizePasskeySignInResponseCallback)callback;
 #endif
 
 /** @fn revokeToken:callback:
@@ -700,7 +721,6 @@ typedef void (^FIRStartPasskeySignInResponseCallback)(
 - (void)startPasskeyEnrollment:(FIRStartPasskeyEnrollmentRequest *)request
                       callback:(FIRStartPasskeyEnrollmentResponseCallback)callback;
 
-
 /** @fn finalizePasskeyEnrollment:callback:
     @brief Calls the finalizePasskeyEnrollment endpoint, which is responsible for sending the
    platform credential details to GCIP backend to exchange the access token and refresh token.
@@ -717,6 +737,14 @@ typedef void (^FIRStartPasskeySignInResponseCallback)(
  */
 - (void)startPasskeySignIn:(FIRStartPasskeySignInRequest *)request
                   callback:(FIRStartPasskeySignInResponseCallback)callback;
+
+/** @fn finalizePasskeySignIn:callback:
+    @brief Sends the platform created public info to the finalizePasskeySignIn endpoint.
+    @param request The request parameters.
+    @param callback The callback.
+ */
+- (void)finalizePasskeySignIn:(FIRFinalizePasskeySignInRequest *)request
+                     callback:(FIRFinalizePasskeySignInResponseCallback)callback;
 #endif
 
 /** @fn revokeToken:callback:
diff --git a/FirebaseAuth/Sources/Backend/FIRAuthBackend.m b/FirebaseAuth/Sources/Backend/FIRAuthBackend.m
index 3ac9f8f2115..d4a55549c58 100644
--- a/FirebaseAuth/Sources/Backend/FIRAuthBackend.m
+++ b/FirebaseAuth/Sources/Backend/FIRAuthBackend.m
@@ -38,6 +38,8 @@
 #import "FirebaseAuth/Sources/Backend/RPC/FIREmailLinkSignInResponse.h"
 #import "FirebaseAuth/Sources/Backend/RPC/FIRFinalizePasskeyEnrollmentRequest.h"
 #import "FirebaseAuth/Sources/Backend/RPC/FIRFinalizePasskeyEnrollmentResponse.h"
+#import "FirebaseAuth/Sources/Backend/RPC/FIRFinalizePasskeySignInRequest.h"
+#import "FirebaseAuth/Sources/Backend/RPC/FIRFinalizePasskeySignInResponse.h"
 #import "FirebaseAuth/Sources/Backend/RPC/FIRGetAccountInfoRequest.h"
 #import "FirebaseAuth/Sources/Backend/RPC/FIRGetAccountInfoResponse.h"
 #import "FirebaseAuth/Sources/Backend/RPC/FIRGetOOBConfirmationCodeRequest.h"
@@ -685,6 +687,11 @@ + (void)startPasskeySignIn:(FIRStartPasskeySignInRequest *)request
   [[self implementation] startPasskeySignIn:request callback:callback];
 }
 
++ (void)finalizePasskeySignIn:(FIRFinalizePasskeySignInRequest *)request
+                     callback:(FIRFinalizePasskeySignInResponseCallback)callback {
+  [[self implementation] finalizePasskeySignIn:request callback:callback];
+}
+
 + (void)startPasskeyEnrollment:(FIRStartPasskeyEnrollmentRequest *)request
                       callback:(FIRStartPasskeyEnrollmentResponseCallback)callback {
   [[self implementation] startPasskeyEnrollment:request callback:callback];
@@ -1138,6 +1145,20 @@ - (void)startPasskeySignIn:(FIRStartPasskeySignInRequest *)request
                }];
 }
 
+- (void)finalizePasskeySignIn:(FIRFinalizePasskeySignInRequest *)request
+                     callback:(FIRFinalizePasskeySignInResponseCallback)callback {
+  FIRFinalizePasskeySignInResponse *response = [[FIRFinalizePasskeySignInResponse alloc] init];
+  [self callWithRequest:request
+               response:response
+               callback:^(NSError *error) {
+                 if (error) {
+                   callback(nil, error);
+                   return;
+                 }
+                 callback(response, nil);
+               }];
+}
+
 - (void)startPasskeyEnrollment:(FIRStartPasskeyEnrollmentRequest *)request
                       callback:(FIRStartPasskeyEnrollmentResponseCallback)callback {
   FIRStartPasskeyEnrollmentResponse *response = [[FIRStartPasskeyEnrollmentResponse alloc] init];
diff --git a/FirebaseAuth/Sources/Backend/RPC/FIRFinalizePasskeyEnrollmentResponse.h b/FirebaseAuth/Sources/Backend/RPC/FIRFinalizePasskeyEnrollmentResponse.h
index 21c553bf9a8..826ba402ad6 100644
--- a/FirebaseAuth/Sources/Backend/RPC/FIRFinalizePasskeyEnrollmentResponse.h
+++ b/FirebaseAuth/Sources/Backend/RPC/FIRFinalizePasskeyEnrollmentResponse.h
@@ -34,7 +34,7 @@ NS_ASSUME_NONNULL_BEGIN
  @property refershToken
  @brief Refresh token for the authenticated user.
  */
-@property(nonatomic, copy, readonly) NSData *refreshToken;
+@property(nonatomic, copy, readonly) NSString *refreshToken;
 
 @end
 
diff --git a/FirebaseAuth/Sources/Backend/RPC/FIRFinalizePasskeySignInRequest.h b/FirebaseAuth/Sources/Backend/RPC/FIRFinalizePasskeySignInRequest.h
new file mode 100644
index 00000000000..778d3328970
--- /dev/null
+++ b/FirebaseAuth/Sources/Backend/RPC/FIRFinalizePasskeySignInRequest.h
@@ -0,0 +1,66 @@
+/*
+ * 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 FIRFinalizePasskeySignInRequest
+    @brief Represents the parameters for the finalizePasskeySignIn endpoint.
+ */
+@interface FIRFinalizePasskeySignInRequest : FIRIdentityToolkitRequest <FIRAuthRPCRequest>
+
+/**
+ @property credentialID
+ @brief The credential ID.
+ */
+@property(nonatomic, copy, readonly) NSString *credentialID;
+
+/**
+ @property clientDataJson
+ @brief The CollectedClientData object from the authenticator.
+ */
+@property(nonatomic, copy, readonly) NSString *clientDataJson;
+
+/**
+ @property authenticatorData
+ @brief The AuthenticatorData from the authenticator.
+ */
+@property(nonatomic, copy, readonly) NSString *authenticatorData;
+
+/**
+ @property signature
+ @brief The signature from the authenticator.
+ */
+@property(nonatomic, copy, readonly) NSString *signature;
+
+/**
+ @property userID
+ @brief The user handle
+ */
+@property(nonatomic, copy, readonly) NSString *userID;
+
+- (nullable instancetype)initWithCredentialID:(NSString *)credentialID
+                               clientDataJson:(NSString *)clientDataJson
+                            authenticatorData:(NSString *)authenticatorData
+                                    signature:(NSString *)signature
+                                       userID:(NSString *)userID
+                         requestConfiguration:(FIRAuthRequestConfiguration *)requestConfiguration;
+
+@end
+
+NS_ASSUME_NONNULL_END
diff --git a/FirebaseAuth/Sources/Backend/RPC/FIRFinalizePasskeySignInRequest.m b/FirebaseAuth/Sources/Backend/RPC/FIRFinalizePasskeySignInRequest.m
new file mode 100644
index 00000000000..865b5f00983
--- /dev/null
+++ b/FirebaseAuth/Sources/Backend/RPC/FIRFinalizePasskeySignInRequest.m
@@ -0,0 +1,132 @@
+/*
+ * 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/FIRFinalizePasskeySignInRequest.h"
+NS_ASSUME_NONNULL_BEGIN
+
+/**
+ @var kFinalizePasskeySignInEndPoint
+ @brief GCIP endpoint for finalizePasskeySignIn rpc
+ */
+static NSString *const kFinalizePasskeySignInEndPoint = @"accounts/passkeySignIn:finalize";
+
+/**
+ @var kTenantIDKey
+ @brief The key for the tenant id value in the request.
+ */
+static NSString *const kTenantIDKey = @"tenantId";
+
+/**
+ @var kAuthenticatorAuthRespKey
+ @brief The key for authentication response object from the authenticator.
+ */
+static NSString *const kAuthenticatorAuthRespKey = @"authenticatorAuthenticationResponse";
+
+/**
+ @var kCredentialIDKey
+ @brief The key for registered credential identifier.
+ */
+static NSString *const kCredentialIDKey = @"credentialId";
+
+/**
+ @var kAuthAssertionRespKey
+ @brief The key for authentication assertion from the authenticator.
+ */
+static NSString *const kAuthAssertionRespKey = @"authenticatorAssertionResponse";
+
+/**
+ @var kClientDataJsonKey
+ @brief The key for CollectedClientData object from the authenticator.
+ */
+static NSString *const kClientDataJsonKey = @"clientDataJson";
+
+/**
+ @var kAuthenticatorDataKey
+ @brief The key for authenticatorData from the authenticator.
+ */
+static NSString *const kAuthenticatorDataKey = @"authenticatorData";
+
+/**
+ @var kSignatureKey
+ @brief The key for the signature from the authenticator.
+ */
+static NSString *const kSignatureKey = @"signature";
+
+/**
+ @var kUserHandleKey
+ @brief The key for the user handle. This is the same as user ID.
+ */
+static NSString *const kUserHandleKey = @"userHandle";
+
+@implementation FIRFinalizePasskeySignInRequest
+
+- (nullable instancetype)initWithCredentialID:(NSString *)credentialID
+                               clientDataJson:(NSString *)clientDataJson
+                            authenticatorData:(NSString *)authenticatorData
+                                    signature:(NSString *)signature
+                                       userID:(NSString *)userID
+                         requestConfiguration:(FIRAuthRequestConfiguration *)requestConfiguration {
+  self = [super initWithEndpoint:kFinalizePasskeySignInEndPoint
+            requestConfiguration:requestConfiguration];
+  if (self) {
+    self.useIdentityPlatform = YES;
+    _credentialID = credentialID;
+    _clientDataJson = clientDataJson;
+    _authenticatorData = authenticatorData;
+    _signature = signature;
+    _userID = userID;
+  }
+  return self;
+}
+
+- (nullable id)unencodedHTTPRequestBodyWithError:(NSError *__autoreleasing _Nullable *)error {
+  NSMutableDictionary *postBody = [NSMutableDictionary dictionary];
+  NSMutableDictionary *authenticatorAuthResponse = [NSMutableDictionary dictionary];
+  NSMutableDictionary *authAssertionResponse = [NSMutableDictionary dictionary];
+
+  if (self.tenantID) {
+    postBody[kTenantIDKey] = self.tenantID;
+  }
+
+  if (_credentialID) {
+    authenticatorAuthResponse[kCredentialIDKey] = _credentialID;
+  }
+
+  if (_clientDataJson) {
+    authAssertionResponse[kClientDataJsonKey] = _clientDataJson;
+  }
+
+  if (_authenticatorData) {
+    authAssertionResponse[kAuthenticatorDataKey] = _authenticatorData;
+  }
+
+  if (_signature) {
+    authAssertionResponse[kSignatureKey] = _signature;
+  }
+
+  if (_userID) {
+    authAssertionResponse[kUserHandleKey] = _userID;
+  }
+
+  authenticatorAuthResponse[kAuthAssertionRespKey] = authAssertionResponse;
+  postBody[kAuthenticatorAuthRespKey] = authenticatorAuthResponse;
+
+  return [postBody copy];
+}
+
+@end
+
+NS_ASSUME_NONNULL_END
diff --git a/FirebaseAuth/Sources/Backend/RPC/FIRFinalizePasskeySignInResponse.h b/FirebaseAuth/Sources/Backend/RPC/FIRFinalizePasskeySignInResponse.h
new file mode 100644
index 00000000000..ba4b8489b73
--- /dev/null
+++ b/FirebaseAuth/Sources/Backend/RPC/FIRFinalizePasskeySignInResponse.h
@@ -0,0 +1,41 @@
+/*
+ * 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 FIRFinalizePasskeySignInResponse
+ @brief Represents the response from the finalizePasskeySignIn endpoint.
+ */
+@interface FIRFinalizePasskeySignInResponse : NSObject <FIRAuthRPCResponse>
+
+/**
+ @property idToken
+ @brief The user raw access token.
+ */
+@property(nonatomic, readonly, copy) NSString *idToken;
+
+/**
+ @property refershToken
+ @brief Refresh token for the authenticated user.
+ */
+@property(nonatomic, copy, readonly) NSString *refreshToken;
+
+@end
+
+NS_ASSUME_NONNULL_END
diff --git a/FirebaseAuth/Sources/Backend/RPC/FIRFinalizePasskeySignInResponse.m b/FirebaseAuth/Sources/Backend/RPC/FIRFinalizePasskeySignInResponse.m
new file mode 100644
index 00000000000..e409c4e4ff3
--- /dev/null
+++ b/FirebaseAuth/Sources/Backend/RPC/FIRFinalizePasskeySignInResponse.m
@@ -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/RPC/FIRFinalizePasskeySignInResponse.h"
+
+/**
+ @var kIDTokenKey
+ @brief The name of the field in the response JSON for id token.
+ */
+static const NSString *kIdTokenKey = @"idToken";
+
+/**
+ @var kRefreshTokenKey
+ @brief The name of the field in the response JSON for refresh token.
+ */
+static const NSString *kRefreshTokenKey = @"refreshToken";
+
+@implementation FIRFinalizePasskeySignInResponse
+
+- (BOOL)setWithDictionary:(nonnull NSDictionary *)dictionary
+                    error:(NSError *__autoreleasing _Nullable *_Nullable)error {
+  if (dictionary[kIdTokenKey] == nil) {
+    return NO;
+  }
+  if (dictionary[kRefreshTokenKey] == nil) {
+    return NO;
+  }
+
+  _idToken = dictionary[kIdTokenKey];
+  _refreshToken = dictionary[kRefreshTokenKey];
+  return YES;
+}
+
+@end
diff --git a/FirebaseAuth/Tests/Unit/FIRFinalizePasskeySignInRequestTests.m b/FirebaseAuth/Tests/Unit/FIRFinalizePasskeySignInRequestTests.m
new file mode 100644
index 00000000000..6c99343d843
--- /dev/null
+++ b/FirebaseAuth/Tests/Unit/FIRFinalizePasskeySignInRequestTests.m
@@ -0,0 +1,188 @@
+/*
+ * 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/FIRFinalizePasskeySignInRequest.h"
+#import "FirebaseAuth/Sources/Backend/RPC/FIRFinalizePasskeySignInResponse.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/passkeySignIn:finalize?key=APIKey";
+
+/**
+ @var kAuthenticatorAuthRespKey
+ @brief The key for authentication response object from the authenticator.
+ */
+static NSString *const kAuthenticatorAuthRespKey = @"authenticatorAuthenticationResponse";
+
+/**
+ @var kAuthAssertionRespKey
+ @brief The key for authentication assertion from the authenticator.
+ */
+static NSString *const kAuthAssertionRespKey = @"authenticatorAssertionResponse";
+
+/**
+ @var kCredentialID
+ @brief credential ID.
+ */
+static NSString *const kCredentialID = @"testCredentialID";
+
+/**
+ @var kCredentialIDKey
+ @brief credential ID field.
+ */
+static NSString *const kCredentialIDKey = @"credentialId";
+
+/**
+ @var kRawClientDataJSON
+ @brief CollectedClientData object from the authenticator.
+ */
+static NSString *const kRawClientDataJSON = @"testRawClientDataJSON";
+
+/**
+ @var kRawClientDataJSONKey
+ @brief The key for the attestation object from the authenticator.
+ */
+static NSString *const kRawClientDataJSONKey = @"clientDataJson";
+
+/**
+ @var kAuthenticatorData
+ @brief The authenticatorData from the authenticator.
+ */
+static NSString *const kAuthenticatorData = @"TestAuthenticatorData";
+
+/**
+ @var kAuthenticatorDataKey
+ @brief The key for authenticatorData from the authenticator.
+ */
+static NSString *const kAuthenticatorDataKey = @"authenticatorData";
+
+/**
+ @var kSignature
+ @brief The signature from the authenticator
+ */
+static NSString *const kSignature = @"testSignature";
+
+/**
+ @var kSignatureKey
+ @brief The key for the signature from the authenticator.
+ */
+static NSString *const kSignatureKey = @"signature";
+
+/**
+ @var kUserHandle
+ @brief The key for the user handle.
+ */
+static NSString *const kUserHandle = @"testUserHandle";
+
+/**
+ @var kUserHandleKey
+ @brief The key for the user handle.
+ */
+static NSString *const kUserHandleKey = @"userHandle";
+
+/**
+ @class FIRFinalizePasskeySignInRequestTests
+ @brief Tests for @c FIRFinalizePasskeySignInRequest.
+ */
+@interface FIRFinalizePasskeySignInRequestTests : XCTestCase
+@end
+
+@implementation FIRFinalizePasskeySignInRequestTests {
+  /**
+   @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)testFinalizePasskeySignInRequest {
+  if (@available(iOS 15.0, *)) {
+    FIRFinalizePasskeySignInRequest *request =
+        [[FIRFinalizePasskeySignInRequest alloc] initWithCredentialID:kCredentialID
+                                                       clientDataJson:kRawClientDataJSON
+                                                    authenticatorData:kAuthenticatorData
+                                                            signature:kSignature
+                                                               userID:kUserHandle
+                                                 requestConfiguration:_requestConfiguration];
+
+    [FIRAuthBackend finalizePasskeySignIn:request
+                                 callback:^(FIRFinalizePasskeySignInResponse *_Nullable response,
+                                            NSError *_Nullable error){
+                                 }];
+    XCTAssertEqualObjects(_RPCIssuer.requestURL.absoluteString, kExpectedAPIURL);
+    XCTAssertNotNil(_RPCIssuer.decodedRequest);
+    XCTAssertEqualObjects(_RPCIssuer.decodedRequest[kAuthenticatorAuthRespKey][kCredentialIDKey],
+                          kCredentialID);
+    XCTAssertEqualObjects(_RPCIssuer.decodedRequest[kAuthenticatorAuthRespKey]
+                                                   [kAuthAssertionRespKey][kRawClientDataJSONKey],
+                          kRawClientDataJSON);
+    XCTAssertEqualObjects(_RPCIssuer.decodedRequest[kAuthenticatorAuthRespKey]
+                                                   [kAuthAssertionRespKey][kAuthenticatorDataKey],
+                          kAuthenticatorData);
+    XCTAssertEqualObjects(
+        _RPCIssuer.decodedRequest[kAuthenticatorAuthRespKey][kAuthAssertionRespKey][kSignatureKey],
+        kSignature);
+    XCTAssertEqualObjects(
+        _RPCIssuer.decodedRequest[kAuthenticatorAuthRespKey][kAuthAssertionRespKey][kUserHandleKey],
+        kUserHandle);
+  }
+}
+
+@end
+#endif
diff --git a/FirebaseAuth/Tests/Unit/FIRFinalizePasskeySignInResponseTests.m b/FirebaseAuth/Tests/Unit/FIRFinalizePasskeySignInResponseTests.m
new file mode 100644
index 00000000000..cf68fd74376
--- /dev/null
+++ b/FirebaseAuth/Tests/Unit/FIRFinalizePasskeySignInResponseTests.m
@@ -0,0 +1,244 @@
+/*
+ * 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/FIRFinalizePasskeySignInRequest.h"
+#import "FirebaseAuth/Sources/Backend/RPC/FIRFinalizePasskeySignInResponse.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 kRefreshToken
+ @brief Refresh Token
+ */
+static NSString *const kRefreshToken = @"refreshToken";
+
+/**
+ @var kCredentialID
+ @brief credential ID.
+ */
+static NSString *const kCredentialID = @"testCredentialID";
+
+/**
+ @var kRawClientDataJSON
+ @brief CollectedClientData object from the authenticator.
+ */
+static NSString *const kRawClientDataJSON = @"testRawClientDataJSON";
+
+/**
+ @var kAuthenticatorData
+ @brief The authenticatorData from the authenticator.
+ */
+static NSString *const kAuthenticatorData = @"TestAuthenticatorData";
+
+/**
+ @var kSignature
+ @brief The signature from the authenticator
+ */
+static NSString *const kSignature = @"testSignature";
+
+/**
+ @var kUserHandle
+ @brief The key for the user handle.
+ */
+static NSString *const kUserHandle = @"testUserHandle";
+
+/**
+ @class FIRFinalizePasskeySignInResponseTests
+ @brief Tests for @c FIRFinalizePasskeySignInResponse.
+ */
+@interface FIRFinalizePasskeySignInResponseTests : XCTestCase
+@end
+@implementation FIRFinalizePasskeySignInResponseTests {
+  /**
+   @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 testSuccessfulFinalizePasskeySignInResponse
+    @brief This test simulates a successful @c FinalizePasskeySignin flow.
+ */
+- (void)testSuccessfulFinalizePasskeySignInResponse {
+  if (@available(iOS 15.0, *)) {
+    FIRFinalizePasskeySignInRequest *request =
+        [[FIRFinalizePasskeySignInRequest alloc] initWithCredentialID:kCredentialID
+                                                       clientDataJson:kRawClientDataJSON
+                                                    authenticatorData:kAuthenticatorData
+                                                            signature:kSignature
+                                                               userID:kUserHandle
+                                                 requestConfiguration:_requestConfiguration];
+
+    __block BOOL callbackInvoked;
+    __block FIRFinalizePasskeySignInResponse *RPCResponse;
+    __block NSError *RPCError;
+
+    [FIRAuthBackend finalizePasskeySignIn:request
+                                 callback:^(FIRFinalizePasskeySignInResponse *_Nullable response,
+                                            NSError *_Nullable error) {
+                                   callbackInvoked = YES;
+                                   RPCResponse = response;
+                                   RPCError = error;
+                                 }];
+
+    [_RPCIssuer respondWithJSON:@{
+      @"idToken" : kIDToken,
+      @"refreshToken" : kRefreshToken,
+    }];
+
+    XCTAssert(callbackInvoked);
+    XCTAssertNil(RPCError);
+    XCTAssertNotNil(RPCResponse);
+    XCTAssertEqualObjects(RPCResponse.idToken, kIDToken);
+    XCTAssertEqualObjects(RPCResponse.refreshToken, kRefreshToken);
+  }
+}
+
+/** @fn testFinalizePasskeySignInResponseMissingIDTokenError
+    @brief This test simulates an unexpected response returned from server in @c
+   FinalizePasskeySignIn flow.
+ */
+- (void)testFinalizePasskeySignInResponseMissingIDTokenError {
+  if (@available(iOS 15.0, *)) {
+    FIRFinalizePasskeySignInRequest *request =
+        [[FIRFinalizePasskeySignInRequest alloc] initWithCredentialID:kCredentialID
+                                                       clientDataJson:kRawClientDataJSON
+                                                    authenticatorData:kAuthenticatorData
+                                                            signature:kSignature
+                                                               userID:kUserHandle
+                                                 requestConfiguration:_requestConfiguration];
+
+    __block BOOL callbackInvoked;
+    __block FIRFinalizePasskeySignInResponse *RPCResponse;
+    __block NSError *RPCError;
+
+    [FIRAuthBackend finalizePasskeySignIn:request
+                                 callback:^(FIRFinalizePasskeySignInResponse *_Nullable response,
+                                            NSError *_Nullable error) {
+                                   callbackInvoked = YES;
+                                   RPCResponse = response;
+                                   RPCError = error;
+                                 }];
+
+    [_RPCIssuer respondWithJSON:@{
+      @"wrongkey" : @{},
+      @"refreshToken" : kRefreshToken,
+    }];
+    [self errorValidationHelperWithCallbackInvoked:callbackInvoked
+                                          rpcError:RPCError
+                                       rpcResponse:RPCResponse];
+  }
+}
+/** @fn testFinalizePasskeySignInResponseMissingRefreshTokenError
+    @brief This test simulates an unexpected response returned from server in @c
+ FinalizePasskeySignIn flow.
+ */
+- (void)testFinalizePasskeySignInResponseMissingRefreshTokenError {
+  if (@available(iOS 15.0, *)) {
+    FIRFinalizePasskeySignInRequest *request =
+        [[FIRFinalizePasskeySignInRequest alloc] initWithCredentialID:kCredentialID
+                                                       clientDataJson:kRawClientDataJSON
+                                                    authenticatorData:kAuthenticatorData
+                                                            signature:kSignature
+                                                               userID:kUserHandle
+                                                 requestConfiguration:_requestConfiguration];
+
+    __block BOOL callbackInvoked;
+    __block FIRFinalizePasskeySignInResponse *RPCResponse;
+    __block NSError *RPCError;
+
+    [FIRAuthBackend finalizePasskeySignIn:request
+                                 callback:^(FIRFinalizePasskeySignInResponse *_Nullable response,
+                                            NSError *_Nullable error) {
+                                   callbackInvoked = YES;
+                                   RPCResponse = response;
+                                   RPCError = error;
+                                 }];
+
+    [_RPCIssuer respondWithJSON:@{
+      @"wrongkey" : @{},
+      @"idToken" : kIDToken,
+    }];
+    [self errorValidationHelperWithCallbackInvoked:callbackInvoked
+                                          rpcError:RPCError
+                                       rpcResponse:RPCResponse];
+  }
+}
+
+/** @fn errorValidationHelperWithCallbackInvoked:rpcError:rpcResponse:
+    @brief Helper function to validate the unexpected response returned from server in @c
+   FinalizePasskeySignIn flow.
+ */
+- (void)errorValidationHelperWithCallbackInvoked:(BOOL)callbackInvoked
+                                        rpcError:(NSError *)RPCError
+                                     rpcResponse:(FIRFinalizePasskeySignInResponse *)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