diff --git a/.editorconfig b/.editorconfig
index 5bcacc92d..547eadea8 100644
--- a/.editorconfig
+++ b/.editorconfig
@@ -6,6 +6,8 @@ root=true
 
 #### Core EditorConfig Options ####
 
+resharper_replace_auto_property_with_computed_property_highlighting = none
+
 # Indentation and spacing
 indent_size=4
 indent_style=space
@@ -1307,8 +1309,6 @@ resharper_parameter_doesnt_make_any_sense_highlighting=warning
 resharper_parameter_hides_member_highlighting=warning
 resharper_parameter_only_used_for_precondition_check_global_highlighting=suggestion
 resharper_parameter_only_used_for_precondition_check_local_highlighting=warning
-resharper_parameter_type_can_be_enumerable_global_highlighting=hint
-resharper_parameter_type_can_be_enumerable_local_highlighting=hint
 resharper_parameter_value_is_not_used_highlighting=warning
 resharper_partial_method_parameter_name_mismatch_highlighting=warning
 resharper_partial_method_with_single_part_highlighting=warning
@@ -1517,8 +1517,6 @@ resharper_resource_item_not_resolved_highlighting=error
 resharper_resource_not_resolved_highlighting=error
 resharper_resx_not_resolved_highlighting=warning
 resharper_return_from_global_scopet_with_value_highlighting=warning
-resharper_return_type_can_be_enumerable_global_highlighting=hint
-resharper_return_type_can_be_enumerable_local_highlighting=hint
 resharper_return_value_of_pure_method_is_not_used_highlighting=warning
 resharper_safe_cast_is_used_as_type_check_highlighting=suggestion
 resharper_same_imports_with_different_name_highlighting=warning
diff --git a/src/Directory.Build.targets b/src/Directory.Build.targets
index 485aa1932..8a9cab353 100644
--- a/src/Directory.Build.targets
+++ b/src/Directory.Build.targets
@@ -2,7 +2,7 @@
 
     <PropertyGroup>
         <TargetFramework>net8.0</TargetFramework>
-        <FrameworkVersion>8.0.18</FrameworkVersion>
+        <FrameworkVersion>8.0.19</FrameworkVersion>
     </PropertyGroup>
 
     <ItemGroup>
@@ -46,12 +46,12 @@
         <PackageReference Update="Serilog.Sinks.File" Version="7.0.0"/>
 
         <!--unsorted -->
-        <PackageReference Update="FluentAssertions" Version="8.5.0"/>
+        <PackageReference Update="FluentAssertions" Version="8.6.0"/>
         <PackageReference Update="Microsoft.AspNetCore.Authentication.OpenIdConnect" Version="$(FrameworkVersion)"/>
         <PackageReference Update="Microsoft.NET.Test.Sdk" Version="17.14.1"/>
         <PackageReference Update="xunit.v3" Version="3.0.0"/>
-        <PackageReference Update="System.IdentityModel.Tokens.Jwt" Version="8.12.1"/>
-        <PackageReference Update="Microsoft.IdentityModel.Protocols.OpenIdConnect" Version="8.12.1"/>
+        <PackageReference Update="System.IdentityModel.Tokens.Jwt" Version="8.13.1"/>
+        <PackageReference Update="Microsoft.IdentityModel.Protocols.OpenIdConnect" Version="8.13.1"/>
         <PackageReference Update="Newtonsoft.Json" Version="13.0.3"/>
 
     </ItemGroup>
diff --git a/src/IdentityServer4/host/Extensions/ExtensionGrantValidator.cs b/src/IdentityServer4/host/Extensions/ExtensionGrantValidator.cs
index 10ed45ace..c84e1929d 100644
--- a/src/IdentityServer4/host/Extensions/ExtensionGrantValidator.cs
+++ b/src/IdentityServer4/host/Extensions/ExtensionGrantValidator.cs
@@ -27,8 +27,5 @@ public Task ValidateAsync(ExtensionGrantValidationContext context)
         return Task.CompletedTask;
     }
 
-    public string GrantType
-    {
-        get { return "custom"; }
-    }
+    public string GrantType { get; } = "custom";
 }
\ No newline at end of file
diff --git a/src/IdentityServer4/src/Extensions/IEnumerableExtensions.cs b/src/IdentityServer4/src/Extensions/IEnumerableExtensions.cs
index aae250e6b..0983d45ef 100644
--- a/src/IdentityServer4/src/Extensions/IEnumerableExtensions.cs
+++ b/src/IdentityServer4/src/Extensions/IEnumerableExtensions.cs
@@ -5,6 +5,7 @@
 using System;
 using System.Collections.Generic;
 using System.Diagnostics;
+using System.Diagnostics.CodeAnalysis;
 using System.Linq;
 
 #pragma warning disable 1591
@@ -14,19 +15,10 @@ namespace IdentityServer4.Extensions;
 public static class IEnumerableExtensions
 {
     [DebuggerStepThrough]
-    public static bool IsNullOrEmpty<T>(this IEnumerable<T> list)
+    public static bool IsNullOrEmpty<T>([NotNullWhen(false)] this IEnumerable<T>? list)
     {
-        if (list == null)
-        {
-            return true;
-        }
-
-        if (!list.Any())
-        {
-            return true;
-        }
-
-        return false;
+        if (list is null) return true;
+        return !list.Any();
     }
 
     public static bool HasDuplicates<T, TProp>(this IEnumerable<T> list, Func<T, TProp> selector)
@@ -39,6 +31,7 @@ public static bool HasDuplicates<T, TProp>(this IEnumerable<T> list, Func<T, TPr
                 return true;
             }
         }
+
         return false;
     }
 }
\ No newline at end of file
diff --git a/src/IdentityServer4/src/Infrastructure/DistributedCacheStateDataFormatter.cs b/src/IdentityServer4/src/Infrastructure/DistributedCacheStateDataFormatter.cs
index e2de46ea0..24ee67516 100644
--- a/src/IdentityServer4/src/Infrastructure/DistributedCacheStateDataFormatter.cs
+++ b/src/IdentityServer4/src/Infrastructure/DistributedCacheStateDataFormatter.cs
@@ -31,7 +31,7 @@ public DistributedCacheStateDataFormatter(IHttpContextAccessor httpContext, stri
         _name = name;
     }
 
-    private string CacheKeyPrefix => "DistributedCacheStateDataFormatter";
+    private string CacheKeyPrefix { get; } = "DistributedCacheStateDataFormatter";
 
     private IDistributedCache Cache => _httpContext.HttpContext.RequestServices.GetRequiredService<IDistributedCache>();
     private IDataProtector Protector => _httpContext.HttpContext.RequestServices.GetRequiredService<IDataProtectionProvider>().CreateProtector(CacheKeyPrefix, _name);
diff --git a/src/IdentityServer4/src/Models/GrantTypes.cs b/src/IdentityServer4/src/Models/GrantTypes.cs
index d32768357..8b326db74 100644
--- a/src/IdentityServer4/src/Models/GrantTypes.cs
+++ b/src/IdentityServer4/src/Models/GrantTypes.cs
@@ -2,41 +2,29 @@
 // Licensed under the Apache License, Version 2.0. See LICENSE in the project root for license information.
 
 
-using System.Collections.Generic;
-
 #pragma warning disable 1591
 
 namespace IdentityServer4.Models;
 
-public class GrantTypes
+public static class GrantTypes
 {
-    public static ICollection<string> Implicit =>
-        [GrantType.Implicit];
+    public static string[] Implicit => [GrantType.Implicit];
 
-    public static ICollection<string> ImplicitAndClientCredentials =>
-        [GrantType.Implicit, GrantType.ClientCredentials];
+    public static string[] ImplicitAndClientCredentials => [GrantType.Implicit, GrantType.ClientCredentials];
 
-    public static ICollection<string> Code =>
-        [GrantType.AuthorizationCode];
+    public static string[] Code => [GrantType.AuthorizationCode];
 
-    public static ICollection<string> CodeAndClientCredentials =>
-        [GrantType.AuthorizationCode, GrantType.ClientCredentials];
+    public static string[] CodeAndClientCredentials => [GrantType.AuthorizationCode, GrantType.ClientCredentials];
 
-    public static ICollection<string> Hybrid =>
-        [GrantType.Hybrid];
+    public static string[] Hybrid => [GrantType.Hybrid];
 
-    public static ICollection<string> HybridAndClientCredentials =>
-        [GrantType.Hybrid, GrantType.ClientCredentials];
+    public static string[] HybridAndClientCredentials => [GrantType.Hybrid, GrantType.ClientCredentials];
 
-    public static ICollection<string> ClientCredentials =>
-        [GrantType.ClientCredentials];
+    public static string[] ClientCredentials => [GrantType.ClientCredentials];
 
-    public static ICollection<string> ResourceOwnerPassword =>
-        [GrantType.ResourceOwnerPassword];
+    public static string[] ResourceOwnerPassword => [GrantType.ResourceOwnerPassword];
 
-    public static ICollection<string> ResourceOwnerPasswordAndClientCredentials =>
-        [GrantType.ResourceOwnerPassword, GrantType.ClientCredentials];
+    public static string[] ResourceOwnerPasswordAndClientCredentials => [GrantType.ResourceOwnerPassword, GrantType.ClientCredentials];
 
-    public static ICollection<string> DeviceFlow =>
-        [GrantType.DeviceFlow];
+    public static string[] DeviceFlow => [GrantType.DeviceFlow];
 }
\ No newline at end of file
diff --git a/src/IdentityServer4/src/Services/Default/OidcReturnUrlParser.cs b/src/IdentityServer4/src/Services/Default/OidcReturnUrlParser.cs
index 35eb15470..3b13fa767 100644
--- a/src/IdentityServer4/src/Services/Default/OidcReturnUrlParser.cs
+++ b/src/IdentityServer4/src/Services/Default/OidcReturnUrlParser.cs
@@ -3,14 +3,12 @@
 
 
 using System;
-using System.Collections.Generic;
 using System.Threading.Tasks;
 using IdentityServer4.Models;
 using IdentityServer4.Extensions;
 using IdentityServer4.Validation;
 using Microsoft.Extensions.Logging;
 using IdentityServer4.Stores;
-using System.Collections.Specialized;
 using System.IdentityModel.Tokens.Jwt;
 using System.Linq;
 
diff --git a/src/IdentityServer4/src/Test/TestUser.cs b/src/IdentityServer4/src/Test/TestUser.cs
index c5760d4c5..afd6d144a 100644
--- a/src/IdentityServer4/src/Test/TestUser.cs
+++ b/src/IdentityServer4/src/Test/TestUser.cs
@@ -46,5 +46,5 @@ public class TestUser
     /// <summary>
     /// Gets or sets the claims.
     /// </summary>
-    public ICollection<Claim> Claims { get; set; } = new HashSet<Claim>(new ClaimComparer());
+    public HashSet<Claim> Claims { get; set; } = new(new ClaimComparer());
 }
\ No newline at end of file
diff --git a/src/IdentityServer4/src/Test/TestUserResourceOwnerPasswordValidator.cs b/src/IdentityServer4/src/Test/TestUserResourceOwnerPasswordValidator.cs
index f0fd0131e..1bcd54c94 100644
--- a/src/IdentityServer4/src/Test/TestUserResourceOwnerPasswordValidator.cs
+++ b/src/IdentityServer4/src/Test/TestUserResourceOwnerPasswordValidator.cs
@@ -6,6 +6,7 @@
 using IdentityServer4.Validation;
 using System.Threading.Tasks;
 using System;
+using System.Linq;
 using Microsoft.AspNetCore.Authentication;
 
 namespace IdentityServer4.Test;
@@ -43,7 +44,7 @@ public Task ValidateAsync(ResourceOwnerPasswordValidationContext context)
             context.Result = new GrantValidationResult(
                 user.SubjectId ?? throw new ArgumentException("Subject ID not set", nameof(user.SubjectId)), 
                 OidcConstants.AuthenticationMethods.Password, _clock.UtcNow.UtcDateTime, 
-                user.Claims);
+                user.Claims.ToArray());
         }
 
         return Task.CompletedTask;
diff --git a/src/IdentityServer4/src/Test/TestUserStore.cs b/src/IdentityServer4/src/Test/TestUserStore.cs
index c9de09630..30fa155e5 100644
--- a/src/IdentityServer4/src/Test/TestUserStore.cs
+++ b/src/IdentityServer4/src/Test/TestUserStore.cs
@@ -115,7 +115,7 @@ public TestUser AutoProvisionUser(string provider, string userId, List<Claim> cl
         }
 
         // if no display name was provided, try to construct by first and/or last name
-        if (!filtered.Any(x => x.Type == JwtClaimTypes.Name))
+        if (filtered.All(x => x.Type != JwtClaimTypes.Name))
         {
             var first = filtered.FirstOrDefault(x => x.Type == JwtClaimTypes.GivenName)?.Value;
             var last = filtered.FirstOrDefault(x => x.Type == JwtClaimTypes.FamilyName)?.Value;
@@ -146,7 +146,7 @@ public TestUser AutoProvisionUser(string provider, string userId, List<Claim> cl
             Username = name,
             ProviderName = provider,
             ProviderSubjectId = userId,
-            Claims = filtered
+            Claims = filtered.ToHashSet()
         };
 
         // add user to in-memory store
diff --git a/src/IdentityServer4/src/Validation/Default/ExtensionGrantValidator.cs b/src/IdentityServer4/src/Validation/Default/ExtensionGrantValidator.cs
index 99bb8d29b..eb9a574c8 100644
--- a/src/IdentityServer4/src/Validation/Default/ExtensionGrantValidator.cs
+++ b/src/IdentityServer4/src/Validation/Default/ExtensionGrantValidator.cs
@@ -5,8 +5,8 @@
 using IdentityServer4.Models;
 using Microsoft.Extensions.Logging;
 using System;
+using System.Collections.Frozen;
 using System.Collections.Generic;
-using System.Linq;
 using System.Threading.Tasks;
 
 namespace IdentityServer4.Validation;
@@ -17,7 +17,8 @@ namespace IdentityServer4.Validation;
 public class ExtensionGrantValidator
 {
     private readonly ILogger _logger;
-    private readonly IEnumerable<IExtensionGrantValidator> _validators;
+    private readonly FrozenSet<string> _availableGrantTypes;
+    private readonly FrozenDictionary<string, IExtensionGrantValidator> _validators;
 
     /// <summary>
     /// Initializes a new instance of the <see cref="ExtensionGrantValidator"/> class.
@@ -26,26 +27,17 @@ public class ExtensionGrantValidator
     /// <param name="logger">The logger.</param>
     public ExtensionGrantValidator(IEnumerable<IExtensionGrantValidator> validators, ILogger<ExtensionGrantValidator> logger)
     {
-        if (validators == null)
-        {
-            _validators = [];
-        }
-        else
-        {
-            _validators = validators;
-        }
-
         _logger = logger;
+
+        _validators = validators.ToFrozenDictionary(x => x.GrantType);
+        _availableGrantTypes = _validators.Keys.ToFrozenSet();
     }
 
     /// <summary>
     /// Gets the available grant types.
     /// </summary>
     /// <returns></returns>
-    public IEnumerable<string> GetAvailableGrantTypes()
-    {
-        return _validators.Select(v => v.GrantType);
-    }
+    public FrozenSet<string> GetAvailableGrantTypes() => _availableGrantTypes;
 
     /// <summary>
     /// Validates the request.
@@ -54,9 +46,7 @@ public IEnumerable<string> GetAvailableGrantTypes()
     /// <returns></returns>
     public async Task<GrantValidationResult> ValidateAsync(ValidatedTokenRequest request)
     {
-        var validator = _validators.FirstOrDefault(v => v.GrantType.Equals(request.GrantType, StringComparison.Ordinal));
-
-        if (validator == null)
+        if (!_validators.TryGetValue(request.GrantType, out var validator))
         {
             _logger.LogError("No validator found for grant type");
             return new GrantValidationResult(TokenRequestErrors.UnsupportedGrantType);
@@ -64,19 +54,19 @@ public async Task<GrantValidationResult> ValidateAsync(ValidatedTokenRequest req
 
         try
         {
-            _logger.LogTrace("Calling into custom grant validator: {type}", validator.GetType().FullName);
+            _logger.LogTrace("Calling into custom grant validator: {Type}", validator.GetType().FullName);
 
             var context = new ExtensionGrantValidationContext
             {
                 Request = request
             };
-            
+
             await validator.ValidateAsync(context);
             return context.Result;
         }
         catch (Exception e)
         {
-            _logger.LogError(1, e, "Grant validation error: {message}", e.Message);
+            _logger.LogError(1, e, "Grant validation error: {Message}", e.Message);
             return new GrantValidationResult(TokenRequestErrors.InvalidGrant);
         }
     }
diff --git a/src/IdentityServer4/src/Validation/Default/TokenRequestValidator.cs b/src/IdentityServer4/src/Validation/Default/TokenRequestValidator.cs
index d406b2dda..65fb86b1c 100644
--- a/src/IdentityServer4/src/Validation/Default/TokenRequestValidator.cs
+++ b/src/IdentityServer4/src/Validation/Default/TokenRequestValidator.cs
@@ -589,7 +589,7 @@ private async Task<TokenRequestValidationResult> ValidateExtensionGrantRequestAs
         /////////////////////////////////////////////
         // check if a validator is registered for the grant type
         /////////////////////////////////////////////
-        if (!_extensionGrantValidator.GetAvailableGrantTypes().Contains(_validatedRequest.GrantType, StringComparer.Ordinal))
+        if (!_extensionGrantValidator.GetAvailableGrantTypes().Contains(_validatedRequest.GrantType))
         {
             LogError("No validator is registered for the grant type", new { grantType = _validatedRequest.GrantType });
             return Invalid(OidcConstants.TokenErrors.UnsupportedGrantType);
diff --git a/src/IdentityServer4/src/Validation/Models/GrantValidationResult.cs b/src/IdentityServer4/src/Validation/Models/GrantValidationResult.cs
index 103c79d40..795721331 100644
--- a/src/IdentityServer4/src/Validation/Models/GrantValidationResult.cs
+++ b/src/IdentityServer4/src/Validation/Models/GrantValidationResult.cs
@@ -28,13 +28,13 @@ public class GrantValidationResult : ValidationResult
     /// <summary>
     /// Custom fields for the token response
     /// </summary>
-    public Dictionary<string, object> CustomResponse { get; set; } = new();
+    public Dictionary<string, object>? CustomResponse { get; set; }
 
     /// <summary>
     /// Initializes a new instance of the <see cref="GrantValidationResult"/> class with no subject.
     /// Warning: the resulting access token will only contain the client identity.
     /// </summary>
-    public GrantValidationResult(Dictionary<string, object> customResponse = null)
+    public GrantValidationResult(Dictionary<string, object>? customResponse = null)
     {
         IsError = false;
         CustomResponse = customResponse;
@@ -44,15 +44,19 @@ public GrantValidationResult(Dictionary<string, object> customResponse = null)
     /// Initializes a new instance of the <see cref="GrantValidationResult"/> class with a given principal.
     /// Warning: the principal needs to include the required claims - it is recommended to use the other constructor that does validation.
     /// </summary>
-    public GrantValidationResult(ClaimsPrincipal principal, Dictionary<string, object> customResponse = null)
+    public GrantValidationResult(ClaimsPrincipal principal, Dictionary<string, object>? customResponse = null)
     {
         IsError = false;
 
         if (principal.Identities.Count() != 1) throw new InvalidOperationException("only a single identity supported");
-        if (principal.FindFirst(JwtClaimTypes.Subject) == null) throw new InvalidOperationException("sub claim is missing");
-        if (principal.FindFirst(JwtClaimTypes.IdentityProvider) == null) throw new InvalidOperationException("idp claim is missing");
-        if (principal.FindFirst(JwtClaimTypes.AuthenticationMethod) == null) throw new InvalidOperationException("amr claim is missing");
-        if (principal.FindFirst(JwtClaimTypes.AuthenticationTime) == null) throw new InvalidOperationException("auth_time claim is missing");
+        if (principal.FindFirst(JwtClaimTypes.Subject) == null)
+            throw new InvalidOperationException("sub claim is missing");
+        if (principal.FindFirst(JwtClaimTypes.IdentityProvider) == null)
+            throw new InvalidOperationException("idp claim is missing");
+        if (principal.FindFirst(JwtClaimTypes.AuthenticationMethod) == null)
+            throw new InvalidOperationException("amr claim is missing");
+        if (principal.FindFirst(JwtClaimTypes.AuthenticationTime) == null)
+            throw new InvalidOperationException("auth_time claim is missing");
 
         Subject = principal;
         CustomResponse = customResponse;
@@ -64,7 +68,8 @@ public GrantValidationResult(ClaimsPrincipal principal, Dictionary<string, objec
     /// <param name="error">The error.</param>
     /// <param name="errorDescription">The error description.</param>
     /// <param name="customResponse">Custom response elements</param>
-    public GrantValidationResult(TokenRequestErrors error, string errorDescription = null, Dictionary<string, object> customResponse = null)
+    public GrantValidationResult(TokenRequestErrors error, string? errorDescription = null,
+        Dictionary<string, object>? customResponse = null)
     {
         Error = ConvertTokenErrorEnumToString(error);
         ErrorDescription = errorDescription;
@@ -83,9 +88,9 @@ public GrantValidationResult(TokenRequestErrors error, string errorDescription =
     public GrantValidationResult(
         string subject,
         string authenticationMethod,
-        IEnumerable<Claim> claims = null,
+        Claim[]? claims = null,
         string identityProvider = IdentityServerConstants.LocalIdentityProvider,
-        Dictionary<string, object> customResponse = null)
+        Dictionary<string, object>? customResponse = null)
         : this(subject, authenticationMethod, DateTime.UtcNow, claims, identityProvider, customResponse)
     {
     }
@@ -104,9 +109,9 @@ public GrantValidationResult(
         string subject,
         string authenticationMethod,
         DateTime authTime,
-        IEnumerable<Claim> claims = null,
+        Claim[]? claims = null,
         string identityProvider = IdentityServerConstants.LocalIdentityProvider,
-        Dictionary<string, object> customResponse = null)
+        Dictionary<string, object>? customResponse = null)
     {
         IsError = false;
 
@@ -130,18 +135,15 @@ public GrantValidationResult(
         CustomResponse = customResponse;
     }
 
-    private string ConvertTokenErrorEnumToString(TokenRequestErrors error)
+    private static string ConvertTokenErrorEnumToString(TokenRequestErrors error) => error switch
     {
-        return error switch
-        {
-            TokenRequestErrors.InvalidClient => OidcConstants.TokenErrors.InvalidClient,
-            TokenRequestErrors.InvalidGrant => OidcConstants.TokenErrors.InvalidGrant,
-            TokenRequestErrors.InvalidRequest => OidcConstants.TokenErrors.InvalidRequest,
-            TokenRequestErrors.InvalidScope => OidcConstants.TokenErrors.InvalidScope,
-            TokenRequestErrors.UnauthorizedClient => OidcConstants.TokenErrors.UnauthorizedClient,
-            TokenRequestErrors.UnsupportedGrantType => OidcConstants.TokenErrors.UnsupportedGrantType,
-            TokenRequestErrors.InvalidTarget => OidcConstants.TokenErrors.InvalidTarget,
-            _ => throw new InvalidOperationException("invalid token error")
-        };
-    }
+        TokenRequestErrors.InvalidClient => OidcConstants.TokenErrors.InvalidClient,
+        TokenRequestErrors.InvalidGrant => OidcConstants.TokenErrors.InvalidGrant,
+        TokenRequestErrors.InvalidRequest => OidcConstants.TokenErrors.InvalidRequest,
+        TokenRequestErrors.InvalidScope => OidcConstants.TokenErrors.InvalidScope,
+        TokenRequestErrors.UnauthorizedClient => OidcConstants.TokenErrors.UnauthorizedClient,
+        TokenRequestErrors.UnsupportedGrantType => OidcConstants.TokenErrors.UnsupportedGrantType,
+        TokenRequestErrors.InvalidTarget => OidcConstants.TokenErrors.InvalidTarget,
+        _ => throw new InvalidOperationException("invalid token error")
+    };
 }
\ No newline at end of file
diff --git a/src/IdentityServer4/src/Validation/Models/ValidationResult.cs b/src/IdentityServer4/src/Validation/Models/ValidationResult.cs
index 0b1c15d31..502c9da57 100644
--- a/src/IdentityServer4/src/Validation/Models/ValidationResult.cs
+++ b/src/IdentityServer4/src/Validation/Models/ValidationResult.cs
@@ -31,5 +31,5 @@ public class ValidationResult
     /// <value>
     /// The error description.
     /// </value>
-    public string ErrorDescription { get; set; }
+    public string? ErrorDescription { get; set; }
 }
\ No newline at end of file
diff --git a/src/IdentityServer4/test/IdentityServer.IntegrationTests/Clients/Setup/DynamicParameterExtensionGrantValidator.cs b/src/IdentityServer4/test/IdentityServer.IntegrationTests/Clients/Setup/DynamicParameterExtensionGrantValidator.cs
index eb6835632..5cc35d762 100644
--- a/src/IdentityServer4/test/IdentityServer.IntegrationTests/Clients/Setup/DynamicParameterExtensionGrantValidator.cs
+++ b/src/IdentityServer4/test/IdentityServer.IntegrationTests/Clients/Setup/DynamicParameterExtensionGrantValidator.cs
@@ -58,5 +58,5 @@ public Task ValidateAsync(ExtensionGrantValidationContext context)
         return Task.CompletedTask;
     }
 
-    public string GrantType => "dynamic";
+    public string GrantType { get; } = "dynamic";
 }
\ No newline at end of file
diff --git a/src/IdentityServer4/test/IdentityServer.IntegrationTests/Clients/Setup/ExtensionGrantValidator.cs b/src/IdentityServer4/test/IdentityServer.IntegrationTests/Clients/Setup/ExtensionGrantValidator.cs
index db4f83648..34c3e6992 100644
--- a/src/IdentityServer4/test/IdentityServer.IntegrationTests/Clients/Setup/ExtensionGrantValidator.cs
+++ b/src/IdentityServer4/test/IdentityServer.IntegrationTests/Clients/Setup/ExtensionGrantValidator.cs
@@ -16,28 +16,20 @@ public Task ValidateAsync(ExtensionGrantValidationContext context)
         var credential = context.Request.Raw.Get("custom_credential");
         var extraClaim = context.Request.Raw.Get("extra_claim");
 
-        if (credential != null)
-        {
-            if (extraClaim != null)
-            {
-                context.Result = new GrantValidationResult(
-                    "818727",
-                    claims: [new Claim("extra_claim", extraClaim)],
-                    authenticationMethod: GrantType);
-            }
-            else
-            {
-                context.Result = new GrantValidationResult("818727", GrantType);
-            }
-        }
-        else
+        if (credential is null)
         {
             // custom error message
             context.Result = new GrantValidationResult(TokenRequestErrors.InvalidGrant, "invalid_custom_credential");
+            return Task.CompletedTask;
         }
 
+        context.Result = context.Result = new GrantValidationResult(
+            "818727",
+            claims: extraClaim is not null ? [new Claim("extra_claim", extraClaim)] : null,
+            authenticationMethod: GrantType);
+
         return Task.CompletedTask;
     }
 
-    public string GrantType =>  "custom";
+    public string GrantType { get; } = "custom";
 }
\ No newline at end of file
diff --git a/src/IdentityServer4/test/IdentityServer.IntegrationTests/Clients/Setup/ExtensionGrantValidator2.cs b/src/IdentityServer4/test/IdentityServer.IntegrationTests/Clients/Setup/ExtensionGrantValidator2.cs
index 9588368d0..bccbd9407 100644
--- a/src/IdentityServer4/test/IdentityServer.IntegrationTests/Clients/Setup/ExtensionGrantValidator2.cs
+++ b/src/IdentityServer4/test/IdentityServer.IntegrationTests/Clients/Setup/ExtensionGrantValidator2.cs
@@ -27,5 +27,5 @@ public Task ValidateAsync(ExtensionGrantValidationContext context)
         return Task.CompletedTask;
     }
 
-    public string GrantType => "custom2";
+    public string GrantType { get; } = "custom2";
 }
\ No newline at end of file
diff --git a/src/IdentityServer4/test/IdentityServer.IntegrationTests/Clients/Setup/NoSubjectExtensionGrantValidator.cs b/src/IdentityServer4/test/IdentityServer.IntegrationTests/Clients/Setup/NoSubjectExtensionGrantValidator.cs
index 6829d5269..7a3785a76 100644
--- a/src/IdentityServer4/test/IdentityServer.IntegrationTests/Clients/Setup/NoSubjectExtensionGrantValidator.cs
+++ b/src/IdentityServer4/test/IdentityServer.IntegrationTests/Clients/Setup/NoSubjectExtensionGrantValidator.cs
@@ -27,5 +27,5 @@ public Task ValidateAsync(ExtensionGrantValidationContext context)
         return Task.CompletedTask;
     }
 
-    public string GrantType => "custom.nosubject";
+    public string GrantType { get; } = "custom.nosubject";
 }
\ No newline at end of file
diff --git a/src/IdentityServer4/test/IdentityServer.IntegrationTests/Endpoints/Authorize/JwtRequestAuthorizeTests.cs b/src/IdentityServer4/test/IdentityServer.IntegrationTests/Endpoints/Authorize/JwtRequestAuthorizeTests.cs
index a27c72f38..f0ba24129 100644
--- a/src/IdentityServer4/test/IdentityServer.IntegrationTests/Endpoints/Authorize/JwtRequestAuthorizeTests.cs
+++ b/src/IdentityServer4/test/IdentityServer.IntegrationTests/Endpoints/Authorize/JwtRequestAuthorizeTests.cs
@@ -19,7 +19,6 @@
 using IdentityServer4.Test;
 using Microsoft.IdentityModel.Logging;
 using Microsoft.IdentityModel.Tokens;
-using Newtonsoft.Json;
 using Xunit;
 using JsonSerializer = System.Text.Json.JsonSerializer;