A while back, I had a (somewhat cryptic) post on OGC services and security.  A couple months later, I saw this post on GeoSolution’s site on GeoServer security and the ins and outs of various options, from native to proxied security.  It is quite a bit more nuanced than my own… .  I recommend you read it, even if you don’t use GeoServer– it is enlightening about the specific problems of securing spatial data that go beyond the simple authentication/authorization models that apply to most other datasets.