How to use Linq to Entities in ApplicationOAuthProvider asp.net web api2

this code return error does not support linq to entities, please help me error return is LINQ to Entities does not recognize the method 'System.String get_Item(System.String)' method, and this method cannot be translated into a store expression.

problem in this line ApplicationUser user = dbContext.Users.Where(s => s.UserName == context.UserName && s.Password == context.Password && s.CodeID == data["CodeID"]);

public class ApplicationOAuthProvider : OAuthAuthorizationServerProvider
{
    private readonly string _publicClientId;

    public ApplicationOAuthProvider(string publicClientId)
    {
        if (publicClientId == null)
        {
            throw new ArgumentNullException("publicClientId");
        }

        _publicClientId = publicClientId;
    }

    public override async Task GrantResourceOwnerCredentials(OAuthGrantResourceOwnerCredentialsContext context)
    {
        var userManager = context.OwinContext.GetUserManager<ApplicationUserManager>();
        var data = await context.Request.ReadFormAsync();

        ApplicationUser user = await userManager.FindAsync(context.UserName, context.Password);

        ApplicationDbContext dbContext = new ApplicationDbContext();

        //here problem
        //does not support linq to entities
        ApplicationUser user = dbContext.Users.Where(s => s.UserName == context.UserName &&  s.Password == context.Password && s.CodeID == data["CodeID"]);
        //here problem

        if (user == null)
        {
            context.SetError("invalid_grant", Resources.Resources.Invalid_UsernamePassword);
            return;
        }

        ClaimsIdentity oAuthIdentity = await user.GenerateUserIdentityAsync(userManager,
           OAuthDefaults.AuthenticationType);
        ClaimsIdentity cookiesIdentity = await user.GenerateUserIdentityAsync(userManager,
            CookieAuthenticationDefaults.AuthenticationType);

        AuthenticationProperties properties = CreateProperties(user.UserName);
        AuthenticationTicket ticket = new AuthenticationTicket(oAuthIdentity, properties);
        context.Validated(ticket);
        context.Request.Context.Authentication.SignIn(cookiesIdentity);
    }

    public override Task TokenEndpoint(OAuthTokenEndpointContext context)
    {
        foreach (KeyValuePair<string, string> property in context.Properties.Dictionary)
        {
            context.AdditionalResponseParameters.Add(property.Key, property.Value);
        }

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

    public override Task ValidateClientAuthentication(OAuthValidateClientAuthenticationContext context)
    {
        // Resource owner password credentials does not provide a client ID.
        if (context.ClientId == null)
        {
            context.Validated();
        }

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

    public override Task ValidateClientRedirectUri(OAuthValidateClientRedirectUriContext context)
    {
        if (context.ClientId == _publicClientId)
        {
            Uri expectedRootUri = new Uri(context.Request.Uri, "/");

            if (expectedRootUri.AbsoluteUri == context.RedirectUri)
            {
                context.Validated();
            }
        }

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

    public static AuthenticationProperties CreateProperties(string Username)
    {
        IDictionary<string, string> data = new Dictionary<string, string>
        {
            { "Username", Username }
        };
        return new AuthenticationProperties(data);
    }
}