diff --git a/src/Core/Services/Fido2ClientService.cs b/src/Core/Services/Fido2ClientService.cs
index 025b28412..1f0bea35e 100644
--- a/src/Core/Services/Fido2ClientService.cs
+++ b/src/Core/Services/Fido2ClientService.cs
@@ -5,7 +5,25 @@ namespace Bit.Core.Services
 {
     public class Fido2ClientService : IFido2ClientService
     {
-        public Task<Fido2ClientCreateCredentialResult> CreateCredentialAsync(Fido2ClientCreateCredentialParams createCredentialParams) => throw new NotImplementedException();
+        public Task<Fido2ClientCreateCredentialResult> CreateCredentialAsync(Fido2ClientCreateCredentialParams createCredentialParams) 
+        {
+            if (!createCredentialParams.SameOriginWithAncestors)
+            {
+                throw new Fido2ClientException(
+                    Fido2ClientException.ErrorCode.NotAllowedError,
+                    "Credential creation is now allowed from embedded contexts with different origins.");
+            }
+
+            if (createCredentialParams.User.Id.Length < 1 || createCredentialParams.User.Id.Length > 64)
+            {
+                // TODO: Should we use ArgumentException here instead?
+                throw new Fido2ClientException(
+                    Fido2ClientException.ErrorCode.TypeError,
+                    "The length of user.id is not between 1 and 64 bytes (inclusive).");
+            }
+
+            throw new NotImplementedException();
+        }
 
         public Task<Fido2ClientAssertCredentialResult> AssertCredentialAsync(Fido2ClientAssertCredentialParams assertCredentialParams) => throw new NotImplementedException();
     }
diff --git a/src/Core/Utilities/Fido2/Fido2ClientCreateCredentialParams.cs b/src/Core/Utilities/Fido2/Fido2ClientCreateCredentialParams.cs
index 49668ef38..f138f79d5 100644
--- a/src/Core/Utilities/Fido2/Fido2ClientCreateCredentialParams.cs
+++ b/src/Core/Utilities/Fido2/Fido2ClientCreateCredentialParams.cs
@@ -12,6 +12,7 @@ namespace Bit.Core.Utilities.Fido2
         /// </summary>
         public required string Origin { get; set; }
 
+        // TODO: Check if we actually need this
         /// <summary>
         /// A value which is true if and only if the caller’s environment settings object is same-origin with its ancestors.
         /// It is false if caller is cross-origin.
diff --git a/src/Core/Utilities/Fido2/Fido2ClientException.cs b/src/Core/Utilities/Fido2/Fido2ClientException.cs
new file mode 100644
index 000000000..4fcfa52d3
--- /dev/null
+++ b/src/Core/Utilities/Fido2/Fido2ClientException.cs
@@ -0,0 +1,22 @@
+namespace Bit.Core.Utilities.Fido2
+{
+    public class Fido2ClientException : Exception
+    {
+        public enum ErrorCode 
+        {
+            NotAllowedError,
+            TypeError,
+            SecurityError,
+            UnknownError
+        }
+
+        public readonly ErrorCode Code;
+        public readonly string Reason;
+
+        public Fido2ClientException(ErrorCode code, string reason) : base($"{code} ({reason})")
+        {
+            Code = code;
+            Reason = reason;
+        }
+    }
+}
diff --git a/test/Core.Test/Services/Fido2ClientCreateCredentialTests.cs b/test/Core.Test/Services/Fido2ClientCreateCredentialTests.cs
new file mode 100644
index 000000000..b250234e2
--- /dev/null
+++ b/test/Core.Test/Services/Fido2ClientCreateCredentialTests.cs
@@ -0,0 +1,86 @@
+using System;
+using System.Threading.Tasks;
+using Bit.Core.Services;
+using Bit.Core.Utilities.Fido2;
+using Bit.Test.Common.AutoFixture;
+using Xunit;
+
+namespace Bit.Core.Test.Services
+{
+    public class Fido2ClientCreateCredentialTests : IDisposable
+    {
+        private readonly SutProvider<Fido2ClientService> _sutProvider = new SutProvider<Fido2ClientService>().Create();
+
+        private Fido2ClientCreateCredentialParams _params;
+
+        public Fido2ClientCreateCredentialTests()
+        {
+            _params = new Fido2ClientCreateCredentialParams {
+                Origin = "https://bitwarden.com",
+                SameOriginWithAncestors = true,
+                Attestation = "none",
+                Challenge = RandomBytes(32),
+                PubKeyCredParams = [
+                    new PublicKeyCredentialParameters {
+                        Type = "public-key",
+                        Alg = -7
+                    }
+                ],
+                Rp = new PublicKeyCredentialRpEntity {
+                    Id = "bitwarden.com",
+                    Name = "Bitwarden"
+                },
+                User = new PublicKeyCredentialUserEntity {
+                    Id = RandomBytes(32),
+                    Name = "user@bitwarden.com",
+                    DisplayName = "User"
+                }
+            };
+        }
+
+        public void Dispose() 
+        {
+        }
+
+        [Fact]
+        // Spec: If sameOriginWithAncestors is false, return a "NotAllowedError" DOMException.
+        public async Task CreateCredentialAsync_ThrowsNotAllowedError_SameOriginWithAncestorsIsFalse()
+        {
+            _params.SameOriginWithAncestors = false;
+
+            var exception = await Assert.ThrowsAsync<Fido2ClientException>(() => _sutProvider.Sut.CreateCredentialAsync(_params));
+
+            Assert.Equal(Fido2ClientException.ErrorCode.NotAllowedError, exception.Code);
+        }
+        
+        [Fact]
+        // Spec: If the length of options.user.id is not between 1 and 64 bytes (inclusive) then return a TypeError.
+        public async Task CreateCredentialAsync_ThrowsTypeError_UserIdIsTooSmall()
+        {
+            _params.User.Id = RandomBytes(0);
+
+            var exception = await Assert.ThrowsAsync<Fido2ClientException>(() => _sutProvider.Sut.CreateCredentialAsync(_params));
+
+            Assert.Equal(Fido2ClientException.ErrorCode.TypeError, exception.Code);
+        }
+
+        [Fact]
+        // Spec: If the length of options.user.id is not between 1 and 64 bytes (inclusive) then return a TypeError.
+        public async Task CreateCredentialAsync_ThrowsTypeError_UserIdIsTooLarge()
+        {
+            _params.User.Id = RandomBytes(65);
+
+            var exception = await Assert.ThrowsAsync<Fido2ClientException>(() => _sutProvider.Sut.CreateCredentialAsync(_params));
+
+            Assert.Equal(Fido2ClientException.ErrorCode.TypeError, exception.Code);
+        }
+
+
+        private byte[] RandomBytes(int length)
+        {
+            var bytes = new byte[length];
+            new Random().NextBytes(bytes);
+            return bytes;
+        }
+    }
+}