From 1b43e1814a3fe2f5f50d98f8ed1da19dca53130a Mon Sep 17 00:00:00 2001
From: Akshat Gandhi <54901287+AkshatG6@users.noreply.github.com>
Date: Fri, 5 Sep 2025 11:53:12 -0700
Subject: [PATCH 1/7] Added GIDTokenClaimsInternalOptions Implementation + Unit
 Tests

---
 .../Sources/GIDTokenClaimsInternalOptions.h   | 48 ++++++++++
 .../Sources/GIDTokenClaimsInternalOptions.m   | 76 +++++++++++++++
 .../Sources/Public/GoogleSignIn/GIDSignIn.h   |  2 +
 .../Unit/GIDTokenClaimsInternalOptionsTest.m  | 92 +++++++++++++++++++
 4 files changed, 218 insertions(+)
 create mode 100644 GoogleSignIn/Sources/GIDTokenClaimsInternalOptions.h
 create mode 100644 GoogleSignIn/Sources/GIDTokenClaimsInternalOptions.m
 create mode 100644 GoogleSignIn/Tests/Unit/GIDTokenClaimsInternalOptionsTest.m

diff --git a/GoogleSignIn/Sources/GIDTokenClaimsInternalOptions.h b/GoogleSignIn/Sources/GIDTokenClaimsInternalOptions.h
new file mode 100644
index 00000000..7cc4153e
--- /dev/null
+++ b/GoogleSignIn/Sources/GIDTokenClaimsInternalOptions.h
@@ -0,0 +1,48 @@
+/*
+ * 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/Foundation.h>
+
+@class GIDTokenClaim;
+
+NS_ASSUME_NONNULL_BEGIN
+
+extern NSString *const kTokenClaimErrorDescription;
+
+extern NSString *const kTokenClaimEssentialPropertyKeyName;
+extern NSString *const kTokenClaimKeyName;
+
+/**
+ * An internal utility class for processing and serializing the NSSet of GIDTokenClaim objects
+ * into the JSON format required for an OIDAuthorizationRequest.
+ */
+@interface GIDTokenClaimsInternalOptions : NSObject
+
+/**
+ * Processes the NSSet of GIDTokenClaim objects, handling ambiguous claims, and returns a JSON string.
+ *
+ * @param claims The NSSet of GIDTokenClaim objects provided by the developer.
+ * @param error A pointer to an NSError object to be populated if an error occurs (e.g., if a
+ * claim is requested as both essential and non-essential).
+ * @return A JSON string representing the claims request, or nil if the input is empty or an
+ * error occurs.
+ */
++ (nullable NSString *)validatedJSONStringForClaims:(nullable NSSet<GIDTokenClaim *> *)claims
+                                              error:(NSError **)error;
+
+@end
+
+NS_ASSUME_NONNULL_END
diff --git a/GoogleSignIn/Sources/GIDTokenClaimsInternalOptions.m b/GoogleSignIn/Sources/GIDTokenClaimsInternalOptions.m
new file mode 100644
index 00000000..037a95e0
--- /dev/null
+++ b/GoogleSignIn/Sources/GIDTokenClaimsInternalOptions.m
@@ -0,0 +1,76 @@
+/*
+ * 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 "GIDTokenClaimsInternalOptions.h"
+#import "GoogleSignIn/Sources/Public/GoogleSignIn/GIDTokenClaim.h"
+#import "GoogleSignIn/Sources/Public/GoogleSignIn/GIDSignIn.h"
+
+NSString * const kTokenClaimErrorDescription = @"The claim was requested as both essential and non-essential. Please provide only one version.";
+
+NSString * const kTokenClaimEssentialPropertyKey = @"essential";
+NSString * const kTokenClaimKeyName = @"id_token";
+
+@implementation GIDTokenClaimsInternalOptions
+
++ (nullable NSString *)validatedJSONStringForClaims:(nullable NSSet<GIDTokenClaim *> *)claims
+                                              error:(NSError **)error {
+  if (!claims || claims.count == 0) {
+    return nil;
+  }
+
+  // === Step 1: Check for claims with ambiguous essential property. ===
+  NSMutableDictionary<NSString *, GIDTokenClaim *> *validTokenClaims =
+  [[NSMutableDictionary alloc] init];
+
+  for (GIDTokenClaim *currentClaim in claims) {
+    GIDTokenClaim *existingClaim = validTokenClaims[currentClaim.name];
+
+    // Check for a conflict: a claim with the same name but different essentiality.
+    if (existingClaim && existingClaim.isEssential != currentClaim.isEssential) {
+      if (error) {
+        *error = [NSError errorWithDomain:kGIDSignInErrorDomain
+                                     code:kGIDSignInErrorCodeAmbiguousClaims
+                                 userInfo:@{NSLocalizedDescriptionKey: kTokenClaimErrorDescription}];
+      }
+      return nil; // Validation failed
+    }
+    validTokenClaims[currentClaim.name] = currentClaim;
+  }
+
+  // === Step 2: Build the dictionary structure required for OIDC JSON ===
+  NSMutableDictionary<NSString *, id> *tokenClaimsDictionary = [[NSMutableDictionary alloc] init];
+  for (GIDTokenClaim *claim in validTokenClaims.allValues) {
+    if (claim.isEssential) {
+      tokenClaimsDictionary[claim.name] = @{ kTokenClaimEssentialPropertyKey: @YES };
+    } else {
+      // Per OIDC spec, non-essential claims can be represented by null.
+      tokenClaimsDictionary[claim.name] = [NSNull null];
+    }
+  }
+  NSDictionary<NSString *, id> *finalRequestDictionary = @{ kTokenClaimKeyName: tokenClaimsDictionary };
+
+  // === Step 3: Serialize the final dictionary into a JSON string ===
+  NSData *jsonData = [NSJSONSerialization dataWithJSONObject:finalRequestDictionary
+                                                     options:0
+                                                       error:error];
+  if (!jsonData) {
+    return nil;
+  }
+
+  return [[NSString alloc] initWithData:jsonData encoding:NSUTF8StringEncoding];
+}
+
+@end
diff --git a/GoogleSignIn/Sources/Public/GoogleSignIn/GIDSignIn.h b/GoogleSignIn/Sources/Public/GoogleSignIn/GIDSignIn.h
index 1025a92a..b147d908 100644
--- a/GoogleSignIn/Sources/Public/GoogleSignIn/GIDSignIn.h
+++ b/GoogleSignIn/Sources/Public/GoogleSignIn/GIDSignIn.h
@@ -45,6 +45,8 @@ typedef NS_ERROR_ENUM(kGIDSignInErrorDomain, GIDSignInErrorCode) {
   kGIDSignInErrorCodeCanceled = -5,
   /// Indicates an Enterprise Mobility Management related error has occurred.
   kGIDSignInErrorCodeEMM = -6,
+  /// Indicates a claim was requested as both essential and non-essential .
+  kGIDSignInErrorCodeAmbiguousClaims = -7,
   /// Indicates the requested scopes have already been granted to the `currentUser`.
   kGIDSignInErrorCodeScopesAlreadyGranted = -8,
   /// Indicates there is an operation on a previous user.
diff --git a/GoogleSignIn/Tests/Unit/GIDTokenClaimsInternalOptionsTest.m b/GoogleSignIn/Tests/Unit/GIDTokenClaimsInternalOptionsTest.m
new file mode 100644
index 00000000..a3b6da44
--- /dev/null
+++ b/GoogleSignIn/Tests/Unit/GIDTokenClaimsInternalOptionsTest.m
@@ -0,0 +1,92 @@
+//
+//  GIDTokenClaimsInternalOptionsTest.h
+//  GoogleSignIn
+//
+//  Created by Akshat Gandhi on 9/5/25.
+//
+
+
+#import <XCTest/XCTest.h>
+#import "GoogleSignIn/Sources/GIDTokenClaimsInternalOptions.h"
+#import "GoogleSignIn/Sources/Public/GoogleSignIn/GIDTokenClaim.h"
+
+@import OCMock;
+
+static NSString *const kEssentialAuthTimeExpectedJSON = @"{\"id_token\":{\"auth_time\":{\"essential\":true}}}";
+static NSString *const kNonEssentialAuthTimeExpectedJSON = @"{\"id_token\":{\"auth_time\":null}}";
+
+
+@interface GIDTokenClaimsInternalOptionsTest : XCTestCase
+@end
+
+@implementation GIDTokenClaimsInternalOptionsTest
+
+#pragma mark - Input Validation Tests
+
+- (void)testValidatedJSONStringForClaims_WithNilInput_ShouldReturnNil {
+  XCTAssertNil([GIDTokenClaimsInternalOptions validatedJSONStringForClaims:nil error:nil]);
+}
+
+- (void)testValidatedJSONStringForClaims_WithEmptyInput_ShouldReturnNil {
+  XCTAssertNil([GIDTokenClaimsInternalOptions validatedJSONStringForClaims:[NSSet set] error:nil]);
+}
+
+#pragma mark - Correct Formatting Tests
+
+- (void)testValidatedJSONStringForClaims_WithNonEssentialClaim_IsCorrectlyFormatted {
+  NSSet *claims = [NSSet setWithObject:[GIDTokenClaim authTimeClaim]];
+
+  NSError *error = nil;
+  NSString *result = [GIDTokenClaimsInternalOptions validatedJSONStringForClaims:claims error:&error];
+
+  XCTAssertNil(error);
+  XCTAssertEqualObjects(result, kNonEssentialAuthTimeExpectedJSON);
+}
+
+- (void)testValidatedJSONStringForClaims_WithEssentialClaim_IsCorrectlyFormatted {
+  NSSet *claims = [NSSet setWithObject:[GIDTokenClaim essentialAuthTimeClaim]];
+
+  NSError *error = nil;
+  NSString *result = [GIDTokenClaimsInternalOptions validatedJSONStringForClaims:claims error:&error];
+
+  XCTAssertNil(error);
+  XCTAssertEqualObjects(result, kEssentialAuthTimeExpectedJSON);
+}
+
+#pragma mark - Client Error Handling Tests
+
+- (void)testValidatedJSONStringForClaims_WithConflictingClaims_ReturnsNilAndPopulatesError {
+  NSSet *claims = [NSSet setWithObjects:[GIDTokenClaim authTimeClaim],
+                                        [GIDTokenClaim essentialAuthTimeClaim],
+                                        nil];
+  NSError *error = nil;
+
+  NSString *result = [GIDTokenClaimsInternalOptions validatedJSONStringForClaims:claims error:&error];
+
+  XCTAssertNil(result, @"Method should return nil for conflicting claims.");
+  XCTAssertNotNil(error, @"An error object should be populated.");
+  XCTAssertEqualObjects(error.domain, kGIDSignInErrorDomain, @"Error domain should be correct.");
+  XCTAssertEqual(error.code, kGIDSignInErrorCodeAmbiguousClaims, @"Error code should be for ambiguous claims.");
+}
+
+- (void)testValidatedJSONStringForClaims_WhenSerializationFails_ReturnsNilAndError {
+  NSSet *claims = [NSSet setWithObject:[GIDTokenClaim authTimeClaim]];
+  NSError *fakeJSONError = [NSError errorWithDomain:@"com.fake.json" code:-999 userInfo:nil];
+  id mockSerialization = OCMClassMock([NSJSONSerialization class]);
+
+  OCMStub([mockSerialization dataWithJSONObject:OCMOCK_ANY
+                                         options:0
+                                           error:[OCMArg setTo:fakeJSONError]]).andReturn(nil);
+
+  NSError *actualError = nil;
+  NSString *result =
+      [GIDTokenClaimsInternalOptions validatedJSONStringForClaims:claims error:&actualError];
+
+  XCTAssertNil(result, @"The result should be nil when JSON serialization fails.");
+  XCTAssertEqualObjects(actualError, fakeJSONError,
+                        @"The error from serialization should be passed back to the caller.");
+
+  [mockSerialization stopMocking];
+}
+
+@end

From e9454a6c647667ac7155fde8eed244c56e4b5509 Mon Sep 17 00:00:00 2001
From: Akshat Gandhi <54901287+AkshatG6@users.noreply.github.com>
Date: Fri, 5 Sep 2025 14:32:06 -0700
Subject: [PATCH 2/7] Added header files to GIDTokenClaimsInternalOptions

---
 GoogleSignIn/Tests/Unit/GIDTokenClaimsInternalOptionsTest.m | 1 +
 1 file changed, 1 insertion(+)

diff --git a/GoogleSignIn/Tests/Unit/GIDTokenClaimsInternalOptionsTest.m b/GoogleSignIn/Tests/Unit/GIDTokenClaimsInternalOptionsTest.m
index a3b6da44..72637a34 100644
--- a/GoogleSignIn/Tests/Unit/GIDTokenClaimsInternalOptionsTest.m
+++ b/GoogleSignIn/Tests/Unit/GIDTokenClaimsInternalOptionsTest.m
@@ -9,6 +9,7 @@
 #import <XCTest/XCTest.h>
 #import "GoogleSignIn/Sources/GIDTokenClaimsInternalOptions.h"
 #import "GoogleSignIn/Sources/Public/GoogleSignIn/GIDTokenClaim.h"
+#import "GoogleSignIn/Sources/Public/GoogleSignIn/GIDSignIn.h"
 
 @import OCMock;
 

From 351afc4371ff1976de71ba071ad3e7c580a225f3 Mon Sep 17 00:00:00 2001
From: Akshat Gandhi <54901287+AkshatG6@users.noreply.github.com>
Date: Mon, 8 Sep 2025 15:55:32 -0700
Subject: [PATCH 3/7] Replaced OCMock with Fake impl to support unit testing
 within GIDTokenClaimsInternalOptions

---
 .../GIDJSONSerializer/API/GIDJSONSerializer.h | 38 ++++++++++
 .../Fake/GIDFakeJSONSerializerImpl.h          | 35 ++++++++++
 .../Fake/GIDFakeJSONSerializerImpl.m          | 40 +++++++++++
 .../Implementation/GIDJSONSerializerImpl.h    | 26 +++++++
 .../Implementation/GIDJSONSerializerImpl.m    | 46 ++++++++++++
 .../Sources/GIDTokenClaimsInternalOptions.h   | 29 +++++---
 .../Sources/GIDTokenClaimsInternalOptions.m   | 61 ++++++++++------
 .../Sources/Public/GoogleSignIn/GIDSignIn.h   |  2 +
 .../Unit/GIDTokenClaimsInternalOptionsTest.m  | 70 +++++++++++--------
 9 files changed, 283 insertions(+), 64 deletions(-)
 create mode 100644 GoogleSignIn/Sources/GIDJSONSerializer/API/GIDJSONSerializer.h
 create mode 100644 GoogleSignIn/Sources/GIDJSONSerializer/Fake/GIDFakeJSONSerializerImpl.h
 create mode 100644 GoogleSignIn/Sources/GIDJSONSerializer/Fake/GIDFakeJSONSerializerImpl.m
 create mode 100644 GoogleSignIn/Sources/GIDJSONSerializer/Implementation/GIDJSONSerializerImpl.h
 create mode 100644 GoogleSignIn/Sources/GIDJSONSerializer/Implementation/GIDJSONSerializerImpl.m

diff --git a/GoogleSignIn/Sources/GIDJSONSerializer/API/GIDJSONSerializer.h b/GoogleSignIn/Sources/GIDJSONSerializer/API/GIDJSONSerializer.h
new file mode 100644
index 00000000..06187949
--- /dev/null
+++ b/GoogleSignIn/Sources/GIDJSONSerializer/API/GIDJSONSerializer.h
@@ -0,0 +1,38 @@
+/*
+ * 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/Foundation.h>
+
+NS_ASSUME_NONNULL_BEGIN
+
+/**
+ * A protocol for serializing an `NSDictionary` into a JSON string.
+ */
+@protocol GIDJSONSerializer <NSObject>
+
+/**
+ * Serializes the given dictionary into a `JSON` string.
+ *
+ * @param jsonObject The dictionary to be serialized.
+ * @param error A pointer to an `NSError` object to be populated upon failure.
+ * @return A `JSON` string representation of the dictionary, or `nil` if an error occurs.
+ */
+- (nullable NSString *)stringWithJSONObject:(NSDictionary<NSString *, id> *)jsonObject
+                                      error:(NSError *_Nullable *_Nullable)error;
+
+@end
+
+NS_ASSUME_NONNULL_END
diff --git a/GoogleSignIn/Sources/GIDJSONSerializer/Fake/GIDFakeJSONSerializerImpl.h b/GoogleSignIn/Sources/GIDJSONSerializer/Fake/GIDFakeJSONSerializerImpl.h
new file mode 100644
index 00000000..65380c4e
--- /dev/null
+++ b/GoogleSignIn/Sources/GIDJSONSerializer/Fake/GIDFakeJSONSerializerImpl.h
@@ -0,0 +1,35 @@
+/*
+ * 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 "GoogleSignIn/Sources/GIDJSONSerializer/API/GIDJSONSerializer.h"
+
+NS_ASSUME_NONNULL_BEGIN
+
+/** A fake implementation of `GIDJSONSerializer` for testing purposes. */
+@interface GIDFakeJSONSerializerImpl : NSObject <GIDJSONSerializer>
+
+/**
+ * The error to be returned by `stringWithJSONObject:error:`.
+ * If `nil`, the method will attempt to perform a real serialization.
+ */
+@property(nonatomic, nullable) NSError *errorToReturn;
+
+/** The dictionary passed to the serialization method. */
+@property(nonatomic, readonly, nullable) NSDictionary<NSString *, id> *capturedJSONObject;
+
+@end
+
+NS_ASSUME_NONNULL_END
diff --git a/GoogleSignIn/Sources/GIDJSONSerializer/Fake/GIDFakeJSONSerializerImpl.m b/GoogleSignIn/Sources/GIDJSONSerializer/Fake/GIDFakeJSONSerializerImpl.m
new file mode 100644
index 00000000..6b887176
--- /dev/null
+++ b/GoogleSignIn/Sources/GIDJSONSerializer/Fake/GIDFakeJSONSerializerImpl.m
@@ -0,0 +1,40 @@
+/*
+ * 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 "GoogleSignIn/Sources/GIDJSONSerializer/Fake/GIDFakeJSONSerializerImpl.h"
+
+@implementation GIDFakeJSONSerializerImpl
+
+- (nullable NSString *)stringWithJSONObject:(NSDictionary<NSString *, id> *)jsonObject
+                                      error:(NSError *_Nullable *_Nullable)error {
+  _capturedJSONObject = [jsonObject copy];
+
+  if (self.errorToReturn) {
+    if (error) {
+      *error = self.errorToReturn;
+    }
+    return nil;
+  }
+  NSData *data = [NSJSONSerialization dataWithJSONObject:jsonObject
+                                                 options:0
+                                                   error:error];
+  if (!data) {
+      return nil;
+  }
+  return [[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding];
+}
+
+@end
diff --git a/GoogleSignIn/Sources/GIDJSONSerializer/Implementation/GIDJSONSerializerImpl.h b/GoogleSignIn/Sources/GIDJSONSerializer/Implementation/GIDJSONSerializerImpl.h
new file mode 100644
index 00000000..5e1eb03d
--- /dev/null
+++ b/GoogleSignIn/Sources/GIDJSONSerializer/Implementation/GIDJSONSerializerImpl.h
@@ -0,0 +1,26 @@
+/*
+ * 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 "GoogleSignIn/Sources/GIDJSONSerializer/API/GIDJSONSerializer.h"
+
+NS_ASSUME_NONNULL_BEGIN
+
+extern NSString *const kGIDJSONSerializationErrorDescription;
+
+@interface GIDJSONSerializerImpl : NSObject <GIDJSONSerializer>
+@end
+
+NS_ASSUME_NONNULL_END
diff --git a/GoogleSignIn/Sources/GIDJSONSerializer/Implementation/GIDJSONSerializerImpl.m b/GoogleSignIn/Sources/GIDJSONSerializer/Implementation/GIDJSONSerializerImpl.m
new file mode 100644
index 00000000..43c76691
--- /dev/null
+++ b/GoogleSignIn/Sources/GIDJSONSerializer/Implementation/GIDJSONSerializerImpl.m
@@ -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 "GoogleSignIn/Sources/GIDJSONSerializer/Implementation/GIDJSONSerializerImpl.h"
+
+#import "GoogleSignIn/Sources/Public/GoogleSignIn/GIDSignIn.h"
+
+NSString * const kGIDJSONSerializationErrorDescription =
+    @"The provided object could not be serialized to a JSON string.";
+
+@implementation GIDJSONSerializerImpl
+
+- (nullable NSString *)stringWithJSONObject:(NSDictionary<NSString *, id> *)jsonObject
+                                      error:(NSError *_Nullable *_Nullable)error {
+  NSError *serializationError = nil;
+  NSData *jsonData = [NSJSONSerialization dataWithJSONObject:jsonObject
+                                                     options:0
+                                                       error:&serializationError];
+  if (!jsonData) {
+    if (error) {
+      *error = [NSError errorWithDomain:kGIDSignInErrorDomain
+                                   code:kGIDSignInErrorCodeJSONSerializationFailure
+                               userInfo:@{
+                            NSLocalizedDescriptionKey:kGIDJSONSerializationErrorDescription,
+                                 NSUnderlyingErrorKey:serializationError
+                               }];
+    }
+    return nil;
+  }
+  return [[NSString alloc] initWithData:jsonData encoding:NSUTF8StringEncoding];
+}
+
+@end
diff --git a/GoogleSignIn/Sources/GIDTokenClaimsInternalOptions.h b/GoogleSignIn/Sources/GIDTokenClaimsInternalOptions.h
index 7cc4153e..adc56dd1 100644
--- a/GoogleSignIn/Sources/GIDTokenClaimsInternalOptions.h
+++ b/GoogleSignIn/Sources/GIDTokenClaimsInternalOptions.h
@@ -20,28 +20,35 @@
 
 NS_ASSUME_NONNULL_BEGIN
 
-extern NSString *const kTokenClaimErrorDescription;
+extern NSString *const kGIDTokenClaimErrorDescription;
+extern NSString *const kGIDTokenClaimEssentialPropertyKeyName;
+extern NSString *const kGIDTokenClaimKeyName;
 
-extern NSString *const kTokenClaimEssentialPropertyKeyName;
-extern NSString *const kTokenClaimKeyName;
+@protocol GIDJSONSerializer;
 
 /**
- * An internal utility class for processing and serializing the NSSet of GIDTokenClaim objects
- * into the JSON format required for an OIDAuthorizationRequest.
+ * An internal utility class for processing and serializing the `NSSet` of `GIDTokenClaim` objects
+ * into the `JSON` format required for an `OIDAuthorizationRequest`.
  */
 @interface GIDTokenClaimsInternalOptions : NSObject
 
+- (instancetype)init;
+
+- (instancetype)initWithJSONSerializer:
+    (id<GIDJSONSerializer>)jsonSerializer NS_DESIGNATED_INITIALIZER;
+
 /**
- * Processes the NSSet of GIDTokenClaim objects, handling ambiguous claims, and returns a JSON string.
+ * Processes the `NSSet` of `GIDTokenClaim` objects, handling ambiguous claims,
+ * and returns a `JSON` string.
  *
- * @param claims The NSSet of GIDTokenClaim objects provided by the developer.
- * @param error A pointer to an NSError object to be populated if an error occurs (e.g., if a
+ * @param claims The `NSSet` of `GIDTokenClaim` objects provided by the developer.
+ * @param error A pointer to an `NSError` object to be populated if an error occurs (e.g., if a
  * claim is requested as both essential and non-essential).
- * @return A JSON string representing the claims request, or nil if the input is empty or an
+ * @return A `JSON` string representing the claims request, or `nil` if the input is empty or an
  * error occurs.
  */
-+ (nullable NSString *)validatedJSONStringForClaims:(nullable NSSet<GIDTokenClaim *> *)claims
-                                              error:(NSError **)error;
+- (nullable NSString *)validatedJSONStringForClaims:(nullable NSSet<GIDTokenClaim *> *)claims
+                                              error:(NSError *_Nullable *_Nullable)error;
 
 @end
 
diff --git a/GoogleSignIn/Sources/GIDTokenClaimsInternalOptions.m b/GoogleSignIn/Sources/GIDTokenClaimsInternalOptions.m
index 037a95e0..049f00e1 100644
--- a/GoogleSignIn/Sources/GIDTokenClaimsInternalOptions.m
+++ b/GoogleSignIn/Sources/GIDTokenClaimsInternalOptions.m
@@ -14,26 +14,45 @@
  * limitations under the License.
  */
 
-#import "GIDTokenClaimsInternalOptions.h"
-#import "GoogleSignIn/Sources/Public/GoogleSignIn/GIDTokenClaim.h"
+#import "GoogleSignIn/Sources/GIDTokenClaimsInternalOptions.h"
+
+#import "GoogleSignIn/Sources/GIDJSONSerializer/API/GIDJSONSerializer.h"
+#import "GoogleSignIn/Sources/GIDJSONSerializer/Implementation/GIDJSONSerializerImpl.h"
 #import "GoogleSignIn/Sources/Public/GoogleSignIn/GIDSignIn.h"
+#import "GoogleSignIn/Sources/Public/GoogleSignIn/GIDTokenClaim.h"
 
-NSString * const kTokenClaimErrorDescription = @"The claim was requested as both essential and non-essential. Please provide only one version.";
+NSString * const kGIDTokenClaimErrorDescription =
+    @"The claim was requested as both essential and non-essential. "
+    @"Please provide only one version.";
+NSString * const kGIDTokenClaimEssentialPropertyKey = @"essential";
+NSString * const kGIDTokenClaimKeyName = @"id_token";
 
-NSString * const kTokenClaimEssentialPropertyKey = @"essential";
-NSString * const kTokenClaimKeyName = @"id_token";
+@interface GIDTokenClaimsInternalOptions ()
+@property(nonatomic, readonly) id<GIDJSONSerializer> jsonSerializer;
+@end
 
 @implementation GIDTokenClaimsInternalOptions
 
-+ (nullable NSString *)validatedJSONStringForClaims:(nullable NSSet<GIDTokenClaim *> *)claims
-                                              error:(NSError **)error {
+- (instancetype)init {
+  return [self initWithJSONSerializer:[[GIDJSONSerializerImpl alloc] init]];
+}
+
+- (instancetype)initWithJSONSerializer:(id<GIDJSONSerializer>)jsonSerializer {
+  if (self = [super init]) {
+    _jsonSerializer = jsonSerializer;
+  }
+  return self;
+}
+
+- (nullable NSString *)validatedJSONStringForClaims:(nullable NSSet<GIDTokenClaim *> *)claims
+                                              error:(NSError *_Nullable *_Nullable)error {
   if (!claims || claims.count == 0) {
     return nil;
   }
 
   // === Step 1: Check for claims with ambiguous essential property. ===
   NSMutableDictionary<NSString *, GIDTokenClaim *> *validTokenClaims =
-  [[NSMutableDictionary alloc] init];
+    [[NSMutableDictionary alloc] init];
 
   for (GIDTokenClaim *currentClaim in claims) {
     GIDTokenClaim *existingClaim = validTokenClaims[currentClaim.name];
@@ -43,34 +62,30 @@ + (nullable NSString *)validatedJSONStringForClaims:(nullable NSSet<GIDTokenClai
       if (error) {
         *error = [NSError errorWithDomain:kGIDSignInErrorDomain
                                      code:kGIDSignInErrorCodeAmbiguousClaims
-                                 userInfo:@{NSLocalizedDescriptionKey: kTokenClaimErrorDescription}];
+                                 userInfo:@{
+                                   NSLocalizedDescriptionKey:kGIDTokenClaimErrorDescription
+                                 }];
       }
-      return nil; // Validation failed
+      return nil;
     }
     validTokenClaims[currentClaim.name] = currentClaim;
   }
 
   // === Step 2: Build the dictionary structure required for OIDC JSON ===
-  NSMutableDictionary<NSString *, id> *tokenClaimsDictionary = [[NSMutableDictionary alloc] init];
+  NSMutableDictionary<NSString *, NSDictionary *> *tokenClaimsDictionary =
+    [[NSMutableDictionary alloc] init];
   for (GIDTokenClaim *claim in validTokenClaims.allValues) {
     if (claim.isEssential) {
-      tokenClaimsDictionary[claim.name] = @{ kTokenClaimEssentialPropertyKey: @YES };
+      tokenClaimsDictionary[claim.name] = @{ kGIDTokenClaimEssentialPropertyKey: @YES };
     } else {
-      // Per OIDC spec, non-essential claims can be represented by null.
-      tokenClaimsDictionary[claim.name] = [NSNull null];
+      tokenClaimsDictionary[claim.name] = @{ kGIDTokenClaimEssentialPropertyKey: @NO };
     }
   }
-  NSDictionary<NSString *, id> *finalRequestDictionary = @{ kTokenClaimKeyName: tokenClaimsDictionary };
+  NSDictionary<NSString *, id> *finalRequestDictionary =
+    @{ kGIDTokenClaimKeyName: tokenClaimsDictionary };
 
   // === Step 3: Serialize the final dictionary into a JSON string ===
-  NSData *jsonData = [NSJSONSerialization dataWithJSONObject:finalRequestDictionary
-                                                     options:0
-                                                       error:error];
-  if (!jsonData) {
-    return nil;
-  }
-
-  return [[NSString alloc] initWithData:jsonData encoding:NSUTF8StringEncoding];
+  return [_jsonSerializer stringWithJSONObject:finalRequestDictionary error:error];
 }
 
 @end
diff --git a/GoogleSignIn/Sources/Public/GoogleSignIn/GIDSignIn.h b/GoogleSignIn/Sources/Public/GoogleSignIn/GIDSignIn.h
index b147d908..29cc0ef7 100644
--- a/GoogleSignIn/Sources/Public/GoogleSignIn/GIDSignIn.h
+++ b/GoogleSignIn/Sources/Public/GoogleSignIn/GIDSignIn.h
@@ -51,6 +51,8 @@ typedef NS_ERROR_ENUM(kGIDSignInErrorDomain, GIDSignInErrorCode) {
   kGIDSignInErrorCodeScopesAlreadyGranted = -8,
   /// Indicates there is an operation on a previous user.
   kGIDSignInErrorCodeMismatchWithCurrentUser = -9,
+  /// Indicates that an object could not be serialized into a `JSON` string.
+  kGIDSignInErrorCodeJSONSerializationFailure = -10
 };
 
 /// This class is used to sign in users with their Google account and manage their session.
diff --git a/GoogleSignIn/Tests/Unit/GIDTokenClaimsInternalOptionsTest.m b/GoogleSignIn/Tests/Unit/GIDTokenClaimsInternalOptionsTest.m
index 72637a34..decea23e 100644
--- a/GoogleSignIn/Tests/Unit/GIDTokenClaimsInternalOptionsTest.m
+++ b/GoogleSignIn/Tests/Unit/GIDTokenClaimsInternalOptionsTest.m
@@ -1,44 +1,62 @@
+// Copyright 2025 Google LLC
 //
-//  GIDTokenClaimsInternalOptionsTest.h
-//  GoogleSignIn
+// 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
 //
-//  Created by Akshat Gandhi on 9/5/25.
+//      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>
+
+#import "GoogleSignIn/Sources/GIDJSONSerializer/Fake/GIDFakeJSONSerializerImpl.h"
 #import "GoogleSignIn/Sources/GIDTokenClaimsInternalOptions.h"
-#import "GoogleSignIn/Sources/Public/GoogleSignIn/GIDTokenClaim.h"
 #import "GoogleSignIn/Sources/Public/GoogleSignIn/GIDSignIn.h"
-
-@import OCMock;
+#import "GoogleSignIn/Sources/Public/GoogleSignIn/GIDTokenClaim.h"
 
 static NSString *const kEssentialAuthTimeExpectedJSON = @"{\"id_token\":{\"auth_time\":{\"essential\":true}}}";
-static NSString *const kNonEssentialAuthTimeExpectedJSON = @"{\"id_token\":{\"auth_time\":null}}";
-
+static NSString *const kNonEssentialAuthTimeExpectedJSON = @"{\"id_token\":{\"auth_time\":{\"essential\":false}}}";
 
 @interface GIDTokenClaimsInternalOptionsTest : XCTestCase
+@property(nonatomic) GIDFakeJSONSerializerImpl *jsonSerializerFake;
+@property(nonatomic) GIDTokenClaimsInternalOptions *tokenClaimsInternalOptions;
 @end
 
 @implementation GIDTokenClaimsInternalOptionsTest
 
+- (void)setUp {
+  [super setUp];
+  _jsonSerializerFake = [[GIDFakeJSONSerializerImpl alloc] init];
+  _tokenClaimsInternalOptions = [[GIDTokenClaimsInternalOptions alloc] initWithJSONSerializer:_jsonSerializerFake];
+}
+
+- (void)tearDown {
+  _jsonSerializerFake = nil;
+  _tokenClaimsInternalOptions = nil;
+  [super tearDown];
+}
+
 #pragma mark - Input Validation Tests
 
 - (void)testValidatedJSONStringForClaims_WithNilInput_ShouldReturnNil {
-  XCTAssertNil([GIDTokenClaimsInternalOptions validatedJSONStringForClaims:nil error:nil]);
+  XCTAssertNil([_tokenClaimsInternalOptions validatedJSONStringForClaims:nil error:nil]);
 }
 
 - (void)testValidatedJSONStringForClaims_WithEmptyInput_ShouldReturnNil {
-  XCTAssertNil([GIDTokenClaimsInternalOptions validatedJSONStringForClaims:[NSSet set] error:nil]);
+  XCTAssertNil([_tokenClaimsInternalOptions validatedJSONStringForClaims:[NSSet set] error:nil]);
 }
 
 #pragma mark - Correct Formatting Tests
 
 - (void)testValidatedJSONStringForClaims_WithNonEssentialClaim_IsCorrectlyFormatted {
   NSSet *claims = [NSSet setWithObject:[GIDTokenClaim authTimeClaim]];
-
   NSError *error = nil;
-  NSString *result = [GIDTokenClaimsInternalOptions validatedJSONStringForClaims:claims error:&error];
+  NSString *result = [_tokenClaimsInternalOptions validatedJSONStringForClaims:claims error:&error];
 
   XCTAssertNil(error);
   XCTAssertEqualObjects(result, kNonEssentialAuthTimeExpectedJSON);
@@ -46,9 +64,8 @@ - (void)testValidatedJSONStringForClaims_WithNonEssentialClaim_IsCorrectlyFormat
 
 - (void)testValidatedJSONStringForClaims_WithEssentialClaim_IsCorrectlyFormatted {
   NSSet *claims = [NSSet setWithObject:[GIDTokenClaim essentialAuthTimeClaim]];
-
   NSError *error = nil;
-  NSString *result = [GIDTokenClaimsInternalOptions validatedJSONStringForClaims:claims error:&error];
+  NSString *result = [_tokenClaimsInternalOptions validatedJSONStringForClaims:claims error:&error];
 
   XCTAssertNil(error);
   XCTAssertEqualObjects(result, kEssentialAuthTimeExpectedJSON);
@@ -60,34 +77,27 @@ - (void)testValidatedJSONStringForClaims_WithConflictingClaims_ReturnsNilAndPopu
   NSSet *claims = [NSSet setWithObjects:[GIDTokenClaim authTimeClaim],
                                         [GIDTokenClaim essentialAuthTimeClaim],
                                         nil];
-  NSError *error = nil;
-
-  NSString *result = [GIDTokenClaimsInternalOptions validatedJSONStringForClaims:claims error:&error];
+  NSError *error;
+  NSString *result = [_tokenClaimsInternalOptions validatedJSONStringForClaims:claims error:&error];
 
   XCTAssertNil(result, @"Method should return nil for conflicting claims.");
   XCTAssertNotNil(error, @"An error object should be populated.");
   XCTAssertEqualObjects(error.domain, kGIDSignInErrorDomain, @"Error domain should be correct.");
-  XCTAssertEqual(error.code, kGIDSignInErrorCodeAmbiguousClaims, @"Error code should be for ambiguous claims.");
+  XCTAssertEqual(error.code, kGIDSignInErrorCodeAmbiguousClaims,
+                 @"Error code should be for ambiguous claims.");
 }
 
 - (void)testValidatedJSONStringForClaims_WhenSerializationFails_ReturnsNilAndError {
   NSSet *claims = [NSSet setWithObject:[GIDTokenClaim authTimeClaim]];
-  NSError *fakeJSONError = [NSError errorWithDomain:@"com.fake.json" code:-999 userInfo:nil];
-  id mockSerialization = OCMClassMock([NSJSONSerialization class]);
-
-  OCMStub([mockSerialization dataWithJSONObject:OCMOCK_ANY
-                                         options:0
-                                           error:[OCMArg setTo:fakeJSONError]]).andReturn(nil);
-
+  NSError *expectedJSONError = [NSError errorWithDomain:@"com.fake.json" code:-999 userInfo:nil];
+  _jsonSerializerFake.errorToReturn = expectedJSONError;
   NSError *actualError = nil;
   NSString *result =
-      [GIDTokenClaimsInternalOptions validatedJSONStringForClaims:claims error:&actualError];
+  [_tokenClaimsInternalOptions validatedJSONStringForClaims:claims error:&actualError];
 
   XCTAssertNil(result, @"The result should be nil when JSON serialization fails.");
-  XCTAssertEqualObjects(actualError, fakeJSONError,
+  XCTAssertEqualObjects(actualError, expectedJSONError,
                         @"The error from serialization should be passed back to the caller.");
-
-  [mockSerialization stopMocking];
 }
 
 @end

From c7a7fb53d5ea8761e1ab063884883b03324f4aec Mon Sep 17 00:00:00 2001
From: Akshat Gandhi <54901287+AkshatG6@users.noreply.github.com>
Date: Mon, 8 Sep 2025 16:17:48 -0700
Subject: [PATCH 4/7] Updated variable names

---
 .../GIDJSONSerializer/Fake/GIDFakeJSONSerializerImpl.m     | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/GoogleSignIn/Sources/GIDJSONSerializer/Fake/GIDFakeJSONSerializerImpl.m b/GoogleSignIn/Sources/GIDJSONSerializer/Fake/GIDFakeJSONSerializerImpl.m
index 6b887176..82bd61dc 100644
--- a/GoogleSignIn/Sources/GIDJSONSerializer/Fake/GIDFakeJSONSerializerImpl.m
+++ b/GoogleSignIn/Sources/GIDJSONSerializer/Fake/GIDFakeJSONSerializerImpl.m
@@ -21,20 +21,19 @@ @implementation GIDFakeJSONSerializerImpl
 - (nullable NSString *)stringWithJSONObject:(NSDictionary<NSString *, id> *)jsonObject
                                       error:(NSError *_Nullable *_Nullable)error {
   _capturedJSONObject = [jsonObject copy];
-
   if (self.errorToReturn) {
     if (error) {
       *error = self.errorToReturn;
     }
     return nil;
   }
-  NSData *data = [NSJSONSerialization dataWithJSONObject:jsonObject
+  NSData *jsonData = [NSJSONSerialization dataWithJSONObject:jsonObject
                                                  options:0
                                                    error:error];
-  if (!data) {
+  if (!jsonData) {
       return nil;
   }
-  return [[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding];
+  return [[NSString alloc] initWithData:jsonData encoding:NSUTF8StringEncoding];
 }
 
 @end

From 3c02be4a9ca77766953b00f02b30910febe83ea3 Mon Sep 17 00:00:00 2001
From: Akshat Gandhi <54901287+AkshatG6@users.noreply.github.com>
Date: Mon, 8 Sep 2025 16:44:25 -0700
Subject: [PATCH 5/7] Removed nil from error initialization in
 GIDTokenClaimsInternalOptionsTest

---
 .../Implementation/GIDJSONSerializerImpl.m                  | 2 +-
 GoogleSignIn/Tests/Unit/GIDTokenClaimsInternalOptionsTest.m | 6 +++---
 2 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/GoogleSignIn/Sources/GIDJSONSerializer/Implementation/GIDJSONSerializerImpl.m b/GoogleSignIn/Sources/GIDJSONSerializer/Implementation/GIDJSONSerializerImpl.m
index 43c76691..8a3e3d84 100644
--- a/GoogleSignIn/Sources/GIDJSONSerializer/Implementation/GIDJSONSerializerImpl.m
+++ b/GoogleSignIn/Sources/GIDJSONSerializer/Implementation/GIDJSONSerializerImpl.m
@@ -25,7 +25,7 @@ @implementation GIDJSONSerializerImpl
 
 - (nullable NSString *)stringWithJSONObject:(NSDictionary<NSString *, id> *)jsonObject
                                       error:(NSError *_Nullable *_Nullable)error {
-  NSError *serializationError = nil;
+  NSError *serializationError;
   NSData *jsonData = [NSJSONSerialization dataWithJSONObject:jsonObject
                                                      options:0
                                                        error:&serializationError];
diff --git a/GoogleSignIn/Tests/Unit/GIDTokenClaimsInternalOptionsTest.m b/GoogleSignIn/Tests/Unit/GIDTokenClaimsInternalOptionsTest.m
index decea23e..047b58a4 100644
--- a/GoogleSignIn/Tests/Unit/GIDTokenClaimsInternalOptionsTest.m
+++ b/GoogleSignIn/Tests/Unit/GIDTokenClaimsInternalOptionsTest.m
@@ -55,7 +55,7 @@ - (void)testValidatedJSONStringForClaims_WithEmptyInput_ShouldReturnNil {
 
 - (void)testValidatedJSONStringForClaims_WithNonEssentialClaim_IsCorrectlyFormatted {
   NSSet *claims = [NSSet setWithObject:[GIDTokenClaim authTimeClaim]];
-  NSError *error = nil;
+  NSError *error;
   NSString *result = [_tokenClaimsInternalOptions validatedJSONStringForClaims:claims error:&error];
 
   XCTAssertNil(error);
@@ -64,7 +64,7 @@ - (void)testValidatedJSONStringForClaims_WithNonEssentialClaim_IsCorrectlyFormat
 
 - (void)testValidatedJSONStringForClaims_WithEssentialClaim_IsCorrectlyFormatted {
   NSSet *claims = [NSSet setWithObject:[GIDTokenClaim essentialAuthTimeClaim]];
-  NSError *error = nil;
+  NSError *error;
   NSString *result = [_tokenClaimsInternalOptions validatedJSONStringForClaims:claims error:&error];
 
   XCTAssertNil(error);
@@ -91,7 +91,7 @@ - (void)testValidatedJSONStringForClaims_WhenSerializationFails_ReturnsNilAndErr
   NSSet *claims = [NSSet setWithObject:[GIDTokenClaim authTimeClaim]];
   NSError *expectedJSONError = [NSError errorWithDomain:@"com.fake.json" code:-999 userInfo:nil];
   _jsonSerializerFake.errorToReturn = expectedJSONError;
-  NSError *actualError = nil;
+  NSError *actualError;
   NSString *result =
   [_tokenClaimsInternalOptions validatedJSONStringForClaims:claims error:&actualError];
 

From 7c12f3f7334c8305cf7b4a6f40cda6c7650aa412 Mon Sep 17 00:00:00 2001
From: Akshat Gandhi <54901287+AkshatG6@users.noreply.github.com>
Date: Tue, 9 Sep 2025 10:05:14 -0700
Subject: [PATCH 6/7] Updated GIDTokenClaimsInternalOptionsTest to test correct
 expected error.

---
 .../Fake/GIDFakeJSONSerializerImpl.h          |  9 +++++---
 .../Fake/GIDFakeJSONSerializerImpl.m          | 15 +++++++++++--
 .../Unit/GIDTokenClaimsInternalOptionsTest.m  | 22 ++++++++++++++-----
 3 files changed, 35 insertions(+), 11 deletions(-)

diff --git a/GoogleSignIn/Sources/GIDJSONSerializer/Fake/GIDFakeJSONSerializerImpl.h b/GoogleSignIn/Sources/GIDJSONSerializer/Fake/GIDFakeJSONSerializerImpl.h
index 65380c4e..fc932577 100644
--- a/GoogleSignIn/Sources/GIDJSONSerializer/Fake/GIDFakeJSONSerializerImpl.h
+++ b/GoogleSignIn/Sources/GIDJSONSerializer/Fake/GIDFakeJSONSerializerImpl.h
@@ -22,10 +22,13 @@ NS_ASSUME_NONNULL_BEGIN
 @interface GIDFakeJSONSerializerImpl : NSObject <GIDJSONSerializer>
 
 /**
- * The error to be returned by `stringWithJSONObject:error:`.
- * If `nil`, the method will attempt to perform a real serialization.
+ * A flag to control whether the serialization method should fail.
+ *
+ * If set to `YES`, `stringWithJSONObject:error:` will return `nil` and
+ * populate the error parameter with a serialization failure error.
+ * If `NO` (the default), it will attempt a real serialization.
  */
-@property(nonatomic, nullable) NSError *errorToReturn;
+@property(nonatomic, assign) BOOL shouldFailJSONSerialization;
 
 /** The dictionary passed to the serialization method. */
 @property(nonatomic, readonly, nullable) NSDictionary<NSString *, id> *capturedJSONObject;
diff --git a/GoogleSignIn/Sources/GIDJSONSerializer/Fake/GIDFakeJSONSerializerImpl.m b/GoogleSignIn/Sources/GIDJSONSerializer/Fake/GIDFakeJSONSerializerImpl.m
index 82bd61dc..eaa9a960 100644
--- a/GoogleSignIn/Sources/GIDJSONSerializer/Fake/GIDFakeJSONSerializerImpl.m
+++ b/GoogleSignIn/Sources/GIDJSONSerializer/Fake/GIDFakeJSONSerializerImpl.m
@@ -16,17 +16,28 @@
 
 #import "GoogleSignIn/Sources/GIDJSONSerializer/Fake/GIDFakeJSONSerializerImpl.h"
 
+#import "GoogleSignIn/Sources/GIDJSONSerializer/Implementation/GIDJSONSerializerImpl.h"
+#import "GoogleSignIn/Sources/Public/GoogleSignIn/GIDSignIn.h"
+
 @implementation GIDFakeJSONSerializerImpl
 
 - (nullable NSString *)stringWithJSONObject:(NSDictionary<NSString *, id> *)jsonObject
                                       error:(NSError *_Nullable *_Nullable)error {
   _capturedJSONObject = [jsonObject copy];
-  if (self.errorToReturn) {
+
+  // Check the boolean flag to see if we should simulate a failure.
+  if (self.shouldFailJSONSerialization) {
     if (error) {
-      *error = self.errorToReturn;
+      *error = [NSError errorWithDomain:kGIDSignInErrorDomain
+                                   code:kGIDSignInErrorCodeJSONSerializationFailure
+                               userInfo:@{
+                            NSLocalizedDescriptionKey:kGIDJSONSerializationErrorDescription,
+                               }];
     }
     return nil;
   }
+
+  // If not failing, fall back to the real serialization path.
   NSData *jsonData = [NSJSONSerialization dataWithJSONObject:jsonObject
                                                  options:0
                                                    error:error];
diff --git a/GoogleSignIn/Tests/Unit/GIDTokenClaimsInternalOptionsTest.m b/GoogleSignIn/Tests/Unit/GIDTokenClaimsInternalOptionsTest.m
index 047b58a4..fa410f65 100644
--- a/GoogleSignIn/Tests/Unit/GIDTokenClaimsInternalOptionsTest.m
+++ b/GoogleSignIn/Tests/Unit/GIDTokenClaimsInternalOptionsTest.m
@@ -15,6 +15,7 @@
 #import <XCTest/XCTest.h>
 
 #import "GoogleSignIn/Sources/GIDJSONSerializer/Fake/GIDFakeJSONSerializerImpl.h"
+#import "GoogleSignIn/Sources/GIDJSONSerializer/Implementation/GIDJSONSerializerImpl.h"
 #import "GoogleSignIn/Sources/GIDTokenClaimsInternalOptions.h"
 #import "GoogleSignIn/Sources/Public/GoogleSignIn/GIDSignIn.h"
 #import "GoogleSignIn/Sources/Public/GoogleSignIn/GIDTokenClaim.h"
@@ -23,8 +24,10 @@
 static NSString *const kNonEssentialAuthTimeExpectedJSON = @"{\"id_token\":{\"auth_time\":{\"essential\":false}}}";
 
 @interface GIDTokenClaimsInternalOptionsTest : XCTestCase
+
 @property(nonatomic) GIDFakeJSONSerializerImpl *jsonSerializerFake;
 @property(nonatomic) GIDTokenClaimsInternalOptions *tokenClaimsInternalOptions;
+
 @end
 
 @implementation GIDTokenClaimsInternalOptionsTest
@@ -89,15 +92,22 @@ - (void)testValidatedJSONStringForClaims_WithConflictingClaims_ReturnsNilAndPopu
 
 - (void)testValidatedJSONStringForClaims_WhenSerializationFails_ReturnsNilAndError {
   NSSet *claims = [NSSet setWithObject:[GIDTokenClaim authTimeClaim]];
-  NSError *expectedJSONError = [NSError errorWithDomain:@"com.fake.json" code:-999 userInfo:nil];
-  _jsonSerializerFake.errorToReturn = expectedJSONError;
+  NSError *expectedJSONError = [NSError errorWithDomain:kGIDSignInErrorDomain
+                                                   code:kGIDSignInErrorCodeJSONSerializationFailure
+                                               userInfo:@{
+                                                 NSLocalizedDescriptionKey: kGIDJSONSerializationErrorDescription,
+                                               }];
+  _jsonSerializerFake.shouldFailJSONSerialization = YES;
   NSError *actualError;
-  NSString *result =
-  [_tokenClaimsInternalOptions validatedJSONStringForClaims:claims error:&actualError];
+  NSString *result = [_tokenClaimsInternalOptions validatedJSONStringForClaims:claims
+                                                                         error:&actualError];
 
   XCTAssertNil(result, @"The result should be nil when JSON serialization fails.");
-  XCTAssertEqualObjects(actualError, expectedJSONError,
-                        @"The error from serialization should be passed back to the caller.");
+  XCTAssertEqualObjects(
+      actualError,
+      expectedJSONError,
+      @"The error from serialization should be passed back to the caller."
+  );
 }
 
 @end

From 8bd3bf3e308fc3387fc60915ed65269eb6c03cc0 Mon Sep 17 00:00:00 2001
From: Akshat Gandhi <54901287+AkshatG6@users.noreply.github.com>
Date: Tue, 9 Sep 2025 12:44:21 -0700
Subject: [PATCH 7/7] Updated GIDFakeJSONSerializerImpl to accept a seeded
 error instead of a BOOL.

---
 .../GIDJSONSerializer/Fake/GIDFakeJSONSerializerImpl.h |  9 ++++-----
 .../GIDJSONSerializer/Fake/GIDFakeJSONSerializerImpl.m | 10 +++-------
 .../Tests/Unit/GIDTokenClaimsInternalOptionsTest.m     |  2 +-
 3 files changed, 8 insertions(+), 13 deletions(-)

diff --git a/GoogleSignIn/Sources/GIDJSONSerializer/Fake/GIDFakeJSONSerializerImpl.h b/GoogleSignIn/Sources/GIDJSONSerializer/Fake/GIDFakeJSONSerializerImpl.h
index fc932577..469fc36d 100644
--- a/GoogleSignIn/Sources/GIDJSONSerializer/Fake/GIDFakeJSONSerializerImpl.h
+++ b/GoogleSignIn/Sources/GIDJSONSerializer/Fake/GIDFakeJSONSerializerImpl.h
@@ -22,13 +22,12 @@ NS_ASSUME_NONNULL_BEGIN
 @interface GIDFakeJSONSerializerImpl : NSObject <GIDJSONSerializer>
 
 /**
- * A flag to control whether the serialization method should fail.
+ * An error to be returned by `stringWithJSONObject:error:`.
  *
- * If set to `YES`, `stringWithJSONObject:error:` will return `nil` and
- * populate the error parameter with a serialization failure error.
- * If `NO` (the default), it will attempt a real serialization.
+ * If this property is set, `stringWithJSONObject:error:` will return `nil` and
+ * populate the error parameter with this error.
  */
-@property(nonatomic, assign) BOOL shouldFailJSONSerialization;
+@property(nonatomic, nullable) NSError *serializationError;
 
 /** The dictionary passed to the serialization method. */
 @property(nonatomic, readonly, nullable) NSDictionary<NSString *, id> *capturedJSONObject;
diff --git a/GoogleSignIn/Sources/GIDJSONSerializer/Fake/GIDFakeJSONSerializerImpl.m b/GoogleSignIn/Sources/GIDJSONSerializer/Fake/GIDFakeJSONSerializerImpl.m
index eaa9a960..400c06ce 100644
--- a/GoogleSignIn/Sources/GIDJSONSerializer/Fake/GIDFakeJSONSerializerImpl.m
+++ b/GoogleSignIn/Sources/GIDJSONSerializer/Fake/GIDFakeJSONSerializerImpl.m
@@ -25,14 +25,10 @@ - (nullable NSString *)stringWithJSONObject:(NSDictionary<NSString *, id> *)json
                                       error:(NSError *_Nullable *_Nullable)error {
   _capturedJSONObject = [jsonObject copy];
 
-  // Check the boolean flag to see if we should simulate a failure.
-  if (self.shouldFailJSONSerialization) {
+  // Check if a serialization error should be simulated.
+  if (self.serializationError) {
     if (error) {
-      *error = [NSError errorWithDomain:kGIDSignInErrorDomain
-                                   code:kGIDSignInErrorCodeJSONSerializationFailure
-                               userInfo:@{
-                            NSLocalizedDescriptionKey:kGIDJSONSerializationErrorDescription,
-                               }];
+      *error = self.serializationError;
     }
     return nil;
   }
diff --git a/GoogleSignIn/Tests/Unit/GIDTokenClaimsInternalOptionsTest.m b/GoogleSignIn/Tests/Unit/GIDTokenClaimsInternalOptionsTest.m
index fa410f65..4c90998f 100644
--- a/GoogleSignIn/Tests/Unit/GIDTokenClaimsInternalOptionsTest.m
+++ b/GoogleSignIn/Tests/Unit/GIDTokenClaimsInternalOptionsTest.m
@@ -97,7 +97,7 @@ - (void)testValidatedJSONStringForClaims_WhenSerializationFails_ReturnsNilAndErr
                                                userInfo:@{
                                                  NSLocalizedDescriptionKey: kGIDJSONSerializationErrorDescription,
                                                }];
-  _jsonSerializerFake.shouldFailJSONSerialization = YES;
+  _jsonSerializerFake.serializationError = expectedJSONError;
   NSError *actualError;
   NSString *result = [_tokenClaimsInternalOptions validatedJSONStringForClaims:claims
                                                                          error:&actualError];