I have a login-protected website. It's an internal application and it's not avaiable to the general public hence it's not indexed by any search engine.
My application is developed on the Google App Engine.
I would like to add a search engine but obviously without the need to public index it. There's any solution avaiable from Google/Bing/Others for a situation like this?
Have you done this before? What solution did you chose and what are yours results?
Well Google has the Google Search Applicance which is basically a blade server which lives on your internal network and creates a "private" index. But this is meant as an enterprise caliber solution (translation: expensive).
Which framework is your website running on? You may be able to find an indexing/search module.
To answer the latter part of the question... I've used Xapian in a Django based website (via the djapian adapter). It basically creates a full-text index. Results are maybe not as good as Bing or Google would generate but it's still quite good; easy to use API too.