Spent some time working on a little app tonight and we needed to import users from one app to another. We decided we didn’t need any real fancy schmancy authentication… if the user says that their email address is foo@example.com then we’ll believe them and let them participate!
The 3rd party app had an internal url we could fetch exported email addresses from in csv format (with only one column for the addresses) so I just fetched the url, grabbed the emails and hashed each one into couchdb to authenticate against. All done in 17 lines.
Yep… that was easy. 
