LockModel with a TTL Index

LockModel.cs

public class LockModel
{        
    public string Id { get; set; }

    /// <summary>
    /// I'm going to set this to the moment in time when the lock should be cleared.
    /// </summary>
    public DateTime ExpireAt { get; set; }
}

LockProvider.cs

// In our LockProvider constructor...

// Specify a TTL index on the ExpiryPoint field.
collection.Indexes.CreateOne(new CreateIndexModel<LockModel>(
  Builders<LockModel>.IndexKeys.Ascending(l => l.ExpireAt),
  new CreateIndexOptions
  {
    ExpireAfter = TimeSpan.Zero
  }
));