The newer CouchDB-XO_Auth project does this better so I suggest looking at that rather than this.

Facebook Authentication for CouchDB

CouchDB has a number of Authentication modules built in (cookie, default & OAuth) and several open source projects for others such as LDAP and OpenID. This project adds a Facebook authentication module that uses the Facebook authentication API to log people in.

It consists of a CouchDB httpd_global_handler that responds to http GET requests and initiates the Facebook login sequence. Once logged in, the handler requests an access code and retrieves the Facebook profile information via https://graph.Facebook.com/me. The user's Facebook ID can then be used to retrieve the CouchDB users document from the authentication_db to create the CouchDB session. The access code is stored in the user record. If there isn't a matching user record then one is created using the Facebook ID as the username

An error during Facebook login will return HTTP 403 to the original caller.

Example Flow of Control

For our example we assume the app is hosted at my_site.com

The user clicks the link my_site.com/_fb
The _fb page redirects user to Facebook so user can approve the apps access to their details
The user logs into Facebook (if not already logged in) and approves the app (if not already approved). NOTE: If the user was already logged in and has already approved the app then they will be redirected back to your app without needing to type anything.
The user arrives back at the _fb_resp page with a code that allows this module to contact Facebook via the API and request an Access Code. No user interaction required.
Once the Access Code is granted it allows the module to retrieve the users id (used as the couch users username when creating the couch user), and is stored in the users record so that it can be used by the app.
When the couch session expires (the app will have to catch this) you simply need to send the user to _fb again and, because they've already gone thru this route, it should get you all the way back to _fb_resp without any user interaction needed.
The final act is to redirect the user back into the app, a location that is a combination of client_app_uri config directive and the clientapptoken param to _fb.

Build

There is an unsophisticated Makefile with targets for test (requires eunit), compile and install.

In order to compile and install this module you might have to edit the Makefile and change one or more of COUCH_ROOT, _COUCHDB_ERLANG_LIB, COUCHDB_LOCALD and COUCHDB_INIT_SCRIPT values to point to the appropriate directories and file within your couchdb installation.

Installation

You need to copy the beam file to somewhere where couch can find it. That location could be something like couchdb/erlang/lib/couch-1.0.1/ebin/ it depends on where/how you've installed couch.

You'll also need to create a [Facebook app](See http://developer.Facebook.com)

Configuration

You'll need to add an ini file or ini entries in couch config to use this module.

      [httpd_global_handlers]
      _fb = {fb_auth, handle_fb_req}
      _fb_resp = {fb_auth, handle_fb_resp_req}

      [fb]
      scope=offline_access,user_about_me
      client_id=1234567890
      redirect_uri=http://my_awesome_app.com/_fb_resp
      client_secret=1234567890ABCDEF123456789
      destination_db=_users
      client_app_uri=http://my_awesome_app.com/home?

_fb
This is the couch location for the code that redirects the user to Facebook. Pass in a param called clientapptoken if you want something added to the client app redirect at the end of the auth process (for when control is returned to your app).

_fb_resp
This is the couch location that Facebook should redirect back to. This should match the redirect_uri field in the [fb] section.

NOTE: Facebook requires that your site is public. The 'Site URL' setting of the Facebook app needs to be set to your site.

scope A comma separated list of the scope of access required to Facebook by the app. See Facebook dev docs for all the scope names. At least offline_access and user_about_me are required.

client_id
The App ID of your Facebook app

redirect_uri
This is the location that Facebook will be told to return the user to when they're done logging in. This MUST start with the same location that you set for Site URL in the Facebook app

client_secret
DO NOT PUBLISH THIS! It is the App Secret from your Facebook app. It is used behind the scenes to contact Facebook. If anyone gets hold of this they can pretend to be your app. Beware!

destination_db
This is the name of the database that the user record will be created in. This is probably _users , but is configurable in case you want to test the app without risking your existing _users database.

client_app_uri
When _fb_resp has been reached it will then need to return the flow to your app. You control where this redirect location with this setting. Any value passed to the initial _fb_ call param clientapptoken will be appended to this URL.

Licenses

CouchDB-Facebook Authentication is licensed under: Apache License Version 2.0, January 2004 http://www.apache.org/licenses/

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.