GetIdentity

private async Task<ClaimsIdentity> GetIdentity(string username, string password)
{
    var user = await signInManager.UserManager.FindByNameAsync(username);
    if (user != null)
    {
        var check = await signInManager.UserManager.CheckPasswordAsync(user, password);

        if (check)
        {
            var principal = await signInManager.CreateUserPrincipalAsync(user);

            return (ClaimsIdentity)principal.Identity;
        }
    }

    return null;
}