Hidden / dashboard-only blogs are pretty straightforward and "only"
require a valid 'access-token' and 'access-token-secret' for the given
'api-key' and 'api-secret', so that signed OAuth1.0 requests are possible.
Private / password protected blogs on the other hand are a bit
cumbersome. In addition to a valid 'access-token' and
'access-token-secret', they also require the account belonging to those
tokens to be a member of the blog itself. Knowing the password and
entering it in the website isn't enough to access a blog through the
API. Following a private blog is also impossible, so that option can't
work either.