public async Task <User> FindByEmailAsync(string email)
{
if (string.IsNullOrWhiteSpace(email))
{
throw new ArgumentException("Value cannot be null or whitespace.", nameof(email));
}
var users = await _dbContext.GetUsersAsync();
var cursor = await users.FindAsync(u => u.Email == email);
return(await cursor.FirstOrDefaultAsync());
}