Update: Twitter has removed oauth_bridge_code support from the API
At @appworkshop in July @themattharris pre announced @Anywhere oauth_bridge_code support. The official announcement has yet to appear but this blog post provides everything you need to get started.
An @Anywhere oauth_bridge_code can be used to get a long lived OAuth 1.0a access_token for the REST API. This allows sites to use @Anywhere and the REST API while only requiring users to only use one authentication method.
The basics are that after a users completes the sign in process for @Anywhere the browser gets an oauth_bridge_code. This oauth_bridge_code can be passed to the /oauth/access_token API endpoint signed with your applications consumer key and secret. If everything checks out Twitter will return a standard access_token for the REST API.
Now lets see some code!
Lets start with authenticating the user using the direct link method described in Hacking Twitter OAuth. You will need to change the oauth_client_identifier to you applications OAuth 1.0a consumer key (AKA your @Anywhere API key) and oauth_callback_url to a URL authorized for the application.
Redirect the user to that URL will be prompt them to connect with your application before being redirected to the oauth_callback_url. Attached in the oauth_callback_url fragment will be an oauth_access_token and am oauth_bridge_code.
Now make a signed POST request to https://api.twitter.com/oauth/access_token using your applications consumer key and secret.
Awesome! You now have a OAuth 1.0a access_token as if you had used the standard OAuth flow with the @twitterapi.
Lets look at getting the oauth_bridge_code using @Anywhere's connect button. This code is a simple HTML document that displays an @Anywhere connect button and handles authComplete on the users return. The oauthComplete uses @jQuery to post the oauth_bridge_code to convert.php which does the same conversion we already saw.
Catch the POST and convert the oauth_bridge_token to an access_token as described above.
An alternative method to verify @Anywhere users, instead of calling verify_credentials with their access_token, is to compare the sha1 hash of their user_id concatenated with the consumer_secret with the value of the twitter_anywhere_identity cookie.
You can read the source information on the slides @themattharris put together for @appworkshop. Skip to page 51.