Getting a user access token in facebook using Koala - facebook

Question

I am writing a simple procedure that automatically makes a facebook
post. From what I understand, I need to have a "user access token" to
do this. I am using Koala (but the philosophy is similar for other
libraries). Anyway, I create a new OAuth account:
#oauth = Koala::Facebook::OAuth.new(app_id, app_secret, callback_url)
The koala instructions then become somewhat unclear. The next two lines are:
#oauth.url_for_oauth_code # generate authenticating URL
#oauth.get_access_token(code) # fetch the access token once you have the code
Where does the "code" variable come from? It doesn't say in the
documentation. Also, does the "get_access_token" method get an "app
access token" or a "user_access_token"? The method name is not clear.
I tried going to the url that the [url_for_oauth_code] method gave me,
but it gives me no code! Where does the "code" variable come from?

Answer 1

On the front page of Koala it states you need to go through the OAuth process described at http://developers.facebook.com/docs/authentication/ (this is an old link but the content within is valid)
Specifically
#oauth.url_for_oauth_code
https://github.com/arsduo/koala/blob/master/lib/koala/oauth.rb#L85
Generates a URL that you need to direct the user to based on the repo it's something like
https://www.facebook.com/dialog/oauth?
client_id={app-id}&
redirect_uri={redirect-uri}&
scope=email
Based on the documentation https://developers.facebook.com/docs/facebook-login/manually-build-a-login-flow/v2.2#login, when the response_type is omitted the default response type is code. So the above is equivalent to
https://www.facebook.com/dialog/oauth?
client_id={app-id}&
response_type=code&
redirect_uri={redirect-uri}&
scope=email
So on redirect to redirect-uri, this URL will be appended with the code param which you must handle then supply to
#oauth.get_access_token(code)
The access token is a user access token.