diff --git a/modules/identityserver/src/Volo.Abp.IdentityServer.Domain/Volo/Abp/IdentityServer/AbpIdentityServerDomainModule.cs b/modules/identityserver/src/Volo.Abp.IdentityServer.Domain/Volo/Abp/IdentityServer/AbpIdentityServerDomainModule.cs
index 9e36576e56..69a9cfabb9 100644
--- a/modules/identityserver/src/Volo.Abp.IdentityServer.Domain/Volo/Abp/IdentityServer/AbpIdentityServerDomainModule.cs
+++ b/modules/identityserver/src/Volo.Abp.IdentityServer.Domain/Volo/Abp/IdentityServer/AbpIdentityServerDomainModule.cs
@@ -9,6 +9,7 @@ using Volo.Abp.Caching;
 using Volo.Abp.Domain.Entities.Events.Distributed;
 using Volo.Abp.Identity;
 using Volo.Abp.IdentityServer.ApiResources;
+using Volo.Abp.IdentityServer.AspNetIdentity;
 using Volo.Abp.IdentityServer.Clients;
 using Volo.Abp.IdentityServer.Devices;
 using Volo.Abp.IdentityServer.IdentityResources;
@@ -94,6 +95,8 @@ namespace Volo.Abp.IdentityServer
                 identityServerBuilder.AddInMemoryApiResources(configuration.GetSection("IdentityServer:ApiResources"));
                 identityServerBuilder.AddInMemoryIdentityResources(configuration.GetSection("IdentityServer:IdentityResources"));
             }
+
+            identityServerBuilder.AddExtensionGrantValidator<LinkLoginExtensionGrantValidator>();
         }
 
         public override void PostConfigureServices(ServiceConfigurationContext context)
diff --git a/modules/identityserver/src/Volo.Abp.IdentityServer.Domain/Volo/Abp/IdentityServer/AspNetIdentity/LinkLoginExtensionGrantValidator.cs b/modules/identityserver/src/Volo.Abp.IdentityServer.Domain/Volo/Abp/IdentityServer/AspNetIdentity/LinkLoginExtensionGrantValidator.cs
new file mode 100644
index 0000000000..3f4ff7dcf2
--- /dev/null
+++ b/modules/identityserver/src/Volo.Abp.IdentityServer.Domain/Volo/Abp/IdentityServer/AspNetIdentity/LinkLoginExtensionGrantValidator.cs
@@ -0,0 +1,179 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Security.Claims;
+using System.Threading.Tasks;
+using IdentityServer4.Validation;
+using Microsoft.Extensions.Localization;
+using Microsoft.Extensions.Logging;
+using Volo.Abp.Identity;
+using Volo.Abp.IdentityServer.Localization;
+using Volo.Abp.MultiTenancy;
+using Volo.Abp.Security.Claims;
+using Volo.Abp.Users;
+using IdentityUser = Volo.Abp.Identity.IdentityUser;
+
+namespace Volo.Abp.IdentityServer.AspNetIdentity
+{
+    public class LinkLoginExtensionGrantValidator : IExtensionGrantValidator
+    {
+        public const string ExtensionGrantType = "LinkUserLogin";
+
+        public string GrantType => ExtensionGrantType;
+
+        protected ITokenValidator TokenValidator  { get; }
+        protected IdentityLinkUserManager IdentityLinkUserManager { get; }
+        protected ICurrentTenant CurrentTenant { get; }
+        protected ICurrentUser CurrentUser { get; }
+        protected ICurrentPrincipalAccessor CurrentPrincipalAccessor { get; }
+        protected IdentityUserManager UserManager { get; }
+        protected IdentitySecurityLogManager IdentitySecurityLogManager { get; }
+        protected ILogger<LinkLoginExtensionGrantValidator> Logger { get; }
+        protected IStringLocalizer<AbpIdentityServerResource> Localizer { get; }
+
+        public LinkLoginExtensionGrantValidator(
+            ITokenValidator tokenValidator,
+            IdentityLinkUserManager identityLinkUserManager,
+            ICurrentTenant currentTenant,
+            ICurrentUser currentUser,
+            IdentityUserManager userManager,
+            ICurrentPrincipalAccessor currentPrincipalAccessor,
+            IdentitySecurityLogManager identitySecurityLogManager,
+            ILogger<LinkLoginExtensionGrantValidator> logger,
+            IStringLocalizer<AbpIdentityServerResource> localizer)
+        {
+            TokenValidator = tokenValidator;
+            IdentityLinkUserManager = identityLinkUserManager;
+            CurrentTenant = currentTenant;
+            CurrentUser = currentUser;
+            UserManager = userManager;
+            CurrentPrincipalAccessor = currentPrincipalAccessor;
+            IdentitySecurityLogManager = identitySecurityLogManager;
+            Logger = logger;
+            Localizer = localizer;
+        }
+
+        public virtual async Task ValidateAsync(ExtensionGrantValidationContext context)
+        {
+            var accessToken = context.Request.Raw["access_token"];
+            if (accessToken.IsNullOrWhiteSpace())
+            {
+                context.Result = new GrantValidationResult
+                {
+                    IsError = true,
+                    Error = "invalid_access_token"
+                };
+                return;
+            }
+
+            var result = await TokenValidator.ValidateAccessTokenAsync(accessToken);
+            if (result.IsError)
+            {
+                context.Result = new GrantValidationResult
+                {
+                    IsError = true,
+                    Error = result.Error,
+                    ErrorDescription = result.ErrorDescription
+                };
+                return;
+            }
+
+            using (CurrentPrincipalAccessor.Change(result.Claims))
+            {
+                var linkUserId = Guid.Empty;;
+                if (!StringToGuid(context.Request.Raw["LinkUserId"], ref linkUserId))
+                {
+                    context.Result = new GrantValidationResult
+                    {
+                        IsError = true,
+                        Error = "invalid_link_user_id"
+                    };
+                    return;
+                }
+
+                Guid? linkTenantId = null;
+                if (!context.Request.Raw["LinkTenantId"].IsNullOrWhiteSpace())
+                {
+                    if (!StringToGuid(context.Request.Raw["LinkTenantId"], ref linkTenantId))
+                    {
+                        context.Result = new GrantValidationResult
+                        {
+                            IsError = true,
+                            Error = "invalid_link_tenant_id"
+                        };
+                        return;
+                    }
+                }
+
+                var isLinked = await IdentityLinkUserManager.IsLinkedAsync(
+                    new IdentityLinkUserInfo(CurrentUser.GetId(), CurrentTenant.Id),
+                    new IdentityLinkUserInfo(linkUserId, linkTenantId));
+
+                if (isLinked)
+                {
+                    using (CurrentTenant.Change(linkTenantId))
+                    {
+                        var user = await UserManager.GetByIdAsync(linkUserId);
+                        var sub = await UserManager.GetUserIdAsync(user);
+
+                        var additionalClaims = new List<Claim>();
+                        await AddCustomClaimsAsync(additionalClaims, user, context);
+
+                        context.Result = new GrantValidationResult(
+                            sub,
+                            GrantType,
+                            additionalClaims.ToArray()
+                        );
+                    }
+                }
+                else
+                {
+                    context.Result = new GrantValidationResult
+                    {
+                        IsError = true,
+                        //TODO: Localizer error message.
+                        Error = "The_Target_User_Is_Not_Linked_ToYou"
+                    };
+                }
+            }
+        }
+
+        protected virtual Task AddCustomClaimsAsync(List<Claim> customClaims, IdentityUser user, ExtensionGrantValidationContext context)
+        {
+            if (user.TenantId.HasValue)
+            {
+                customClaims.Add(new Claim(AbpClaimTypes.TenantId, user.TenantId?.ToString()));
+            }
+
+            return Task.CompletedTask;
+        }
+
+        protected virtual bool StringToGuid(string str, ref Guid guid)
+        {
+            if (str.IsNullOrWhiteSpace())
+            {
+                return false;
+            }
+
+            if (Guid.TryParse(str, out var g))
+            {
+                guid = g;
+                return true;
+            }
+
+            return false;
+        }
+
+        protected virtual bool StringToGuid(string str, ref Guid? guid)
+        {
+            var g = Guid.Empty;
+            if (StringToGuid(str, ref g))
+            {
+                guid = g;
+                return true;
+            }
+
+            return false;
+        }
+    }
+}