OWIN ASP.NET - Cant generate Access Token using Refresh Token if Access Token is expired

When I try to generate an Access Token using the Refresh Token before Access Token expires, the system generate a new one and everything is okey. But if the Access Token is expired, the request return invalid_grant.

Isn't the Validated() method from GrantRefreshToken generate the Access Token using the identity I stored in the dictionary from the previously Access Token?

And how can I block clients from asking for new Access Token using the same Refresh Token if the last one isn't expired yet?

Here is my code:

Startup.cs:

public partial class Startup
{
    public void Configuration(IAppBuilder app)
    {
        app.UseOAuthAuthorizationServer(new OAuthAuthorizationServerOptions()
        {
            AllowInsecureHttp = true,

            TokenEndpointPath = new PathString("/token"),
            AccessTokenExpireTimeSpan = TimeSpan.FromMinutes(5),

            Provider = new OAuthProvider(),
            RefreshTokenProvider = new RefreshTokenProvider()
        });
        app.UseOAuthBearerAuthentication(new OAuthBearerAuthenticationOptions());
        app.UseWebApi(config);
    }
}

OAuthProvider.cs:

public class OAuthProvider : OAuthAuthorizationServerProvider
{
    public override Task ValidateClientAuthentication(OAuthValidateClientAuthenticationContext context)
    {
        context.Validated();
        return Task.FromResult<object>(null);
    }

    public override Task GrantResourceOwnerCredentials(OAuthGrantResourceOwnerCredentialsContext context)
    {
        if (context.UserName == "admin" && context.Password == "123456")
        {
            var claimsIdentity = new ClaimsIdentity(context.Options.AuthenticationType);
            claimsIdentity.AddClaim(new Claim(ClaimTypes.Name, context.UserName));
            claimsIdentity.AddClaim(new Claim(ClaimTypes.Role, "Admin"));

            var ticket = new AuthenticationTicket(claimsIdentity, null);
            context.Validated(ticket);
        }
        return Task.FromResult<object>(null);
    }

    public override Task GrantRefreshToken(OAuthGrantRefreshTokenContext context)
    {
        context.Validated(context.Ticket);
        return Task.FromResult<object>(null);
    }
}

RefreshTokenProvider.cs:

public class RefreshTokenProvider : AuthenticationTokenProvider
{
    private static ConcurrentDictionary<string, AuthenticationTicket> _refreshTokens = new ConcurrentDictionary<string, AuthenticationTicket>();

    public override Task CreateAsync(AuthenticationTokenCreateContext context)
    {
        var guid = Guid.NewGuid().ToString();
        _refreshTokens.TryAdd(guid, context.Ticket);

        context.SetToken(guid);
        return Task.FromResult<object>(null);
    }

    public override Task ReceiveAsync(AuthenticationTokenReceiveContext context)
    {
        if (_refreshTokens.TryRemove(context.Token, out AuthenticationTicket ticket))
        {
            context.SetTicket(ticket);
        }
        return Task.FromResult<object>(null);
    }
}

Sorry for bad english, I hope you understand!

EDIT:

Well, I modified the code to implement Database support and set the Refresh Token expiration to 5 minutes. The expiration is small for testing purposes.

Here is the result:

OAuthProvider.cs:

public class OAuthProvider : OAuthAuthorizationServerProvider
{
    public override Task ValidateClientAuthentication(OAuthValidateClientAuthenticationContext context)
    {
        context.Validated();
        return Task.FromResult<object>(null);
    }

    public override Task GrantResourceOwnerCredentials(OAuthGrantResourceOwnerCredentialsContext context)
    {
        try
        {
            var account = AccountRepository.Instance.GetByUsername(context.UserName);
            if (account != null && Global.VerifyHash(context.Password, account.Password))
            {
                var claimsIdentity = new ClaimsIdentity(context.Options.AuthenticationType);
                claimsIdentity.AddClaim(new Claim(ClaimTypes.Name, account.Username));
                claimsIdentity.AddClaim(new Claim("DriverId", account.DriverId.ToString()));

                var newTicket = new AuthenticationTicket(claimsIdentity, null);
                context.Validated(newTicket);
            }
        }
        catch { }

        return Task.FromResult<object>(null);
    }

    public override Task GrantRefreshToken(OAuthGrantRefreshTokenContext context)
    {
        context.Validated();
        return Task.FromResult<object>(null);
    }
}

RefreshTokenProvider.cs:

public class RefreshTokenProvider : AuthenticationTokenProvider
{
    public override Task CreateAsync(AuthenticationTokenCreateContext context)
    {
        var refreshToken = new TokenModel()
        {
            Subject = context.Ticket.Identity.Name,
            Token = GenerateToken(),
            IssuedUtc = DateTime.UtcNow,
            ExpiresUtc = DateTime.UtcNow.AddMinutes(5)
        };

        context.Ticket.Properties.IssuedUtc = refreshToken.IssuedUtc;
        context.Ticket.Properties.ExpiresUtc = refreshToken.ExpiresUtc;

        refreshToken.Ticket = context.SerializeTicket();

        try
        {
            TokenRepository.Instance.Insert(refreshToken);
            context.SetToken(refreshToken.Token);
        }
        catch { }

        return Task.FromResult<object>(null);
    }

    public override Task ReceiveAsync(AuthenticationTokenReceiveContext context)
    {
        try
        {
            var refreshToken = TokenRepository.Instance.Get(context.Token);
            if (refreshToken != null)
            {
                if (TokenRepository.Instance.Delete(refreshToken))
                {
                    context.DeserializeTicket(refreshToken.Ticket);
                }
            }
        }
        catch { }

        return Task.FromResult<object>(null);
    }

    private string GenerateToken()
    {
        HashAlgorithm hashAlgorithm = new SHA256CryptoServiceProvider();

        byte[] byteValue = Encoding.UTF8.GetBytes(Guid.NewGuid().ToString("N"));
        byte[] byteHash = hashAlgorithm.ComputeHash(byteValue);

        return Convert.ToBase64String(byteHash);
    }
}

Thanks for the support!