diff --git a/src/Core/Abstractions/IFido2UserInterface.cs b/src/Core/Abstractions/IFido2UserInterface.cs
new file mode 100644
index 0000000000..b01b52d232
--- /dev/null
+++ b/src/Core/Abstractions/IFido2UserInterface.cs
@@ -0,0 +1,46 @@
+using Bit.Core.Utilities.Fido2;
+
+namespace Bit.Core.Abstractions
+{
+    /// <summary>
+    /// Parameters used to ask the user to pick a credential from a list of existing credentials.
+    /// </summary>
+    public struct Fido2PickCredentialParams
+    {
+        /// <summary>
+        /// The IDs of the credentials that the user can pick from.
+        /// </summary>
+        public string[] CipherIds { get; set; }
+
+        /// <summary>
+        /// Whether or not the user must be verified before completing the operation.
+        /// </summary>
+        public bool UserVerification { get; set; }
+    }
+
+    /// <summary>
+    /// The result of asking the user to pick a credential from a list of existing credentials.
+    /// </summary>
+    public struct Fido2PickCredentialResult
+    {
+        /// <summary>
+        /// The ID of the cipher that contains the credentials the user picked.
+        /// </summary>
+        public string CipherId { get; set; }
+
+        /// <summary>
+        /// Whether or not the user was verified before completing the operation.
+        /// </summary>
+        public bool UserVerified { get; set; }
+    }
+
+    public interface IFido2UserInterface
+    {
+        /// <summary>
+        /// Ask the user to pick a credential from a list of existing credentials.
+        /// </summary>
+        /// <param name="pickCredentialParams">The parameters to use when asking the user to pick a credential.</param>
+        /// <returns>The ID of the cipher that contains the credentials the user picked.</returns>
+        Task<Fido2PickCredentialResult> PickCredentialAsync(Fido2PickCredentialParams pickCredentialParams);
+    }
+}
diff --git a/src/Core/Models/View/Fido2CredentialView.cs b/src/Core/Models/View/Fido2CredentialView.cs
index 92d3ff85b7..5086c72d3e 100644
--- a/src/Core/Models/View/Fido2CredentialView.cs
+++ b/src/Core/Models/View/Fido2CredentialView.cs
@@ -29,7 +29,7 @@ namespace Bit.Core.Models.View
 
         public override string SubTitle => UserName;
         public override List<KeyValuePair<string, LinkedIdType>> LinkedFieldOptions => new List<KeyValuePair<string, LinkedIdType>>();
-        public bool IsDiscoverable => !string.IsNullOrWhiteSpace(Discoverable);
+        public bool IsDiscoverable => bool.TryParse(Discoverable, out var isDiscoverable) && isDiscoverable;
         public bool CanLaunch => !string.IsNullOrEmpty(RpId);
         public string LaunchUri => $"https://{RpId}";
 
diff --git a/src/Core/Services/Fido2AuthenticatorService.cs b/src/Core/Services/Fido2AuthenticatorService.cs
index 26a8024f10..fb897044d1 100644
--- a/src/Core/Services/Fido2AuthenticatorService.cs
+++ b/src/Core/Services/Fido2AuthenticatorService.cs
@@ -1,27 +1,95 @@
 using Bit.Core.Abstractions;
+using Bit.Core.Models.View;
+using Bit.Core.Enums;
 using Bit.Core.Utilities.Fido2;
 
 namespace Bit.Core.Services
 {
     public class Fido2AuthenticatorService : IFido2AuthenticatorService
     {
+        private INativeLogService _logService;
         private ICipherService _cipherService;
+        private ISyncService _syncService;
+        private IFido2UserInterface _userInterface;
         
-        public Fido2AuthenticatorService(ICipherService cipherService)
+        public Fido2AuthenticatorService(INativeLogService logService, ICipherService cipherService, ISyncService syncService, IFido2UserInterface userInterface)
         {
+            _logService = logService;
             _cipherService = cipherService;
+            _syncService = syncService;
+            _userInterface = userInterface;
         }
         
-        public Task<Fido2AuthenticatorGetAssertionResult> GetAssertionAsync(Fido2AuthenticatorGetAssertionParams assertionParams)
+        public async Task<Fido2AuthenticatorGetAssertionResult> GetAssertionAsync(Fido2AuthenticatorGetAssertionParams assertionParams)
         {
-            throw new NotAllowedError();
+            // throw new NotAllowedError();
+            List<CipherView> cipherOptions;
+
+            // await userInterfaceSession.ensureUnlockedVault();
+            await _syncService.FullSyncAsync(false);
+
+            if (assertionParams.AllowCredentialDescriptorList?.Length > 0) {
+                cipherOptions = await FindCredentialsById(
+                    assertionParams.AllowCredentialDescriptorList,
+                    assertionParams.RpId
+                );
+            } else {
+                cipherOptions = new List<CipherView>();
+                // cipherOptions = await this.findCredentialsByRp(params.rpId);
+            }
+
+            if (cipherOptions.Count == 0) {
+                _logService.Info(
+                    "[Fido2Authenticator] Aborting because no matching credentials were found in the vault."
+                );
+
+                throw new NotAllowedError();
+            }
+
+            var response = await _userInterface.PickCredentialAsync(new Fido2PickCredentialParams {
+                CipherIds = cipherOptions.Select((cipher) => cipher.Id).ToArray(),
+                UserVerification = assertionParams.RequireUserVerification
+            });
             
             // TODO: IMPLEMENT this
-            // return Task.FromResult(new Fido2AuthenticatorGetAssertionResult
-            // {
-            //     AuthenticatorData = new byte[32],
-            //     Signature = new byte[8]
-            // });
+            return new Fido2AuthenticatorGetAssertionResult
+            {
+                AuthenticatorData = new byte[32],
+                Signature = new byte[8]
+            };
         }
+
+    private async Task<List<CipherView>> FindCredentialsById(PublicKeyCredentialDescriptor[] credentials, string rpId)
+    {
+        var ids = new List<string>();
+
+        foreach (var credential in credentials)
+        {
+            try
+            {
+                ids.Add(GuidToStandardFormat(credential.Id));
+            }
+            catch {}
+        }
+
+        if (ids.Count == 0)
+        {
+            return new List<CipherView>();
+        }
+
+        var ciphers = await _cipherService.GetAllDecryptedAsync();
+        return ciphers.FindAll((cipher) =>
+            !cipher.IsDeleted &&
+            cipher.Type == CipherType.Login &&
+            cipher.Login.HasFido2Credentials &&
+            cipher.Login.Fido2Credentials[0].RpId == rpId &&
+            ids.Contains(cipher.Login.Fido2Credentials[0].CredentialId)
+        );
+    }
+
+    private string GuidToStandardFormat(byte[] bytes)
+    {
+        return new Guid(bytes).ToString();
+    }
     }
 }
diff --git a/test/Core.Test/Services/Fido2AuthenticatorTests.cs b/test/Core.Test/Services/Fido2AuthenticatorTests.cs
index 76b144bf42..577f3a8cdf 100644
--- a/test/Core.Test/Services/Fido2AuthenticatorTests.cs
+++ b/test/Core.Test/Services/Fido2AuthenticatorTests.cs
@@ -5,6 +5,7 @@ using Bit.Core.Exceptions;
 using Bit.Core.Services;
 using Bit.Core.Models.Domain;
 using Bit.Core.Models.View;
+using Bit.Core.Enums;
 using Bit.Core.Test.AutoFixture;
 using Bit.Core.Utilities.Fido2;
 using Bit.Test.Common.AutoFixture;
@@ -14,6 +15,7 @@ using NSubstitute.ExceptionExtensions;
 using Xunit;
 using Bit.Core.Utilities;
 using System.Collections.Generic;
+using System.Linq;
 
 namespace Bit.Core.Test.Services
 {
@@ -33,37 +35,72 @@ namespace Bit.Core.Test.Services
         [InlineCustomAutoData(new[] { typeof(SutProviderCustomization) })]
         public async Task GetAssertionAsync_Throws_CredentialExistsButRpIdDoesNotMatch(SutProvider<Fido2AuthenticatorService> sutProvider, Fido2AuthenticatorGetAssertionParams aParams)
         {
-            var credentialId = RandomBytes(32);
+            var credentialId = Guid.NewGuid();
             aParams.RpId = "bitwarden.com";
             aParams.AllowCredentialDescriptorList = [
                 new PublicKeyCredentialDescriptor {
-                    Id = credentialId,
+                    Id = credentialId.ToByteArray(),
                     Type = "public-key"
                 }
             ];
-            sutProvider.GetDependency<ICipherService>().GetAllDecryptedAsync().Returns(new List<CipherView> {
-                new CipherView {
-                    Login = new LoginView {
-                        Fido2Credentials = new List<Fido2CredentialView> {
-                            new Fido2CredentialView {
-                                CredentialId = CoreHelpers.Base64UrlEncode(credentialId),
-                                RpId = "mismatch-rpid"
-                            }
-                        }
-                    }
-                }
-            });
+            sutProvider.GetDependency<ICipherService>().GetAllDecryptedAsync().Returns([
+                CreateCipherView(credentialId.ToString(), "mismatch-rpid", false),
+            ]);
 
             var exception = await Assert.ThrowsAsync<NotAllowedError>(() => sutProvider.Sut.GetAssertionAsync(aParams));
         }
 
         #endregion
 
+        #region vault contains credential
+
+        [Theory]
+        [InlineCustomAutoData(new[] { typeof(SutProviderCustomization) })]
+        public async Task GetAssertionAsync_AsksForAllCredentials_ParamsContainsAllowedCredentialsList(SutProvider<Fido2AuthenticatorService> sutProvider, Fido2AuthenticatorGetAssertionParams aParams)
+        {
+            var credentialIds = new[] { Guid.NewGuid(), Guid.NewGuid() };
+            List<CipherView> ciphers = [ 
+                CreateCipherView(credentialIds[0].ToString(), "bitwarden.com", false),
+                CreateCipherView(credentialIds[1].ToString(), "bitwarden.com", true)
+            ];
+            aParams.RpId = "bitwarden.com";
+            aParams.AllowCredentialDescriptorList = credentialIds.Select((credentialId) => new PublicKeyCredentialDescriptor {
+                Id = credentialId.ToByteArray(),
+                Type = "public-key"
+            }).ToArray();
+            sutProvider.GetDependency<ICipherService>().GetAllDecryptedAsync().Returns(ciphers);
+
+            await sutProvider.Sut.GetAssertionAsync(aParams);
+
+            await sutProvider.GetDependency<IFido2UserInterface>().Received().PickCredentialAsync(Arg.Is<Fido2PickCredentialParams>(
+                (pickCredentialParams) => pickCredentialParams.CipherIds.SequenceEqual(ciphers.Select((cipher) => cipher.Id)) && pickCredentialParams.UserVerification == aParams.RequireUserVerification
+            ));
+        }
+        
+        #endregion
+
         private byte[] RandomBytes(int length)
         {
             var bytes = new byte[length];
             new Random().NextBytes(bytes);
             return bytes;
         }
+
+        #nullable enable
+        private CipherView CreateCipherView(string? credentialId, string? rpId, bool? discoverable)
+        {
+            return new CipherView {
+                Type = CipherType.Login,
+                Login = new LoginView {
+                    Fido2Credentials = new List<Fido2CredentialView> {
+                        new Fido2CredentialView {
+                            CredentialId = credentialId ?? Guid.NewGuid().ToString(),
+                            RpId = rpId ?? "bitwarden.com",
+                            Discoverable = discoverable.HasValue ? discoverable.ToString() : "true"
+                        }
+                    }
+                }
+            };
+        }
     }
 }