Facebook OAuth with Sinatra

This MOSTLY is working, so, here’s what I found when trying to connect to Facebook with OAuth. It needs some serious refactoring because a lot of this was done in an “investigative” trial and error way. It also looks like Facebook have improved their docs on this since I was first looking at them…

First, you need to initiate a connection:

    get '/:blog_name/facebook/oauth/create' do
      redirect "https://graph.facebook.com/oauth/authorize?client_id=##FACEBOOK API KEY##&redirect_uri=##CALLBACK URL##&scope=publish_stream,user_status,user_photos,user_about_me"
    end

where ##FACEBOOK API KEY## = your applications API key (mine is a 32 digit hex value) and ##CALLBACK URL## = the URL that will be processing the next step. Also, the scope value let’s you get more access to the user’s account. Check their extended permissions doc for more info.

Next, you need to process what comes back from Facebook. I am stashing what comes back in the DB (the FacebookOauthToken model). Also using the Mechanize gem which is pretty silly. Some of the code below is specific to my app, so ignore those bits…

    get '/:blog_name/facebook/oauth/callback' do
      if !params['code'].blank?
        url="https://graph.facebook.com/oauth/access_token"
        client_id="client_id=##CLIENT ID##"
        client_secret="client_secret=## CLIENT SECRET ##"
        code="code=#{URI.escape(params['code'])}"
        redirect_uri="redirect_uri=http://example.org/#{@blog.url_name}/facebook/oauth/callback"
 
        url="#{url}?#{client_id}&#{client_secret}&#{code}&#{redirect_uri}"
        begin
          res=open(url)
        rescue
          flash[:error]="There was a problem connecting to Facebook"
          redirect "/#{@blog.url_name}/"
        end
        read=res.read
        access_token=CGI.parse(read)['access_token']
        if !access_token.blank?
          @blog.facebook_oauth_token = FacebookOauthToken.new(:access_token=>access_token,:blog_name=>params[:blog_name])
          if @blog.save
            begin
              a=Mechanize.new
              res=a.get("https://graph.facebook.com/me/?access_token=#{access_token}")
              @blog.facebook_oauth_token.facebook_id=JSON(res.body)['id']
              @blog.save!
            rescue
              flash[:error]="There was a problem getting information from Facebook"
              redirect "/#{@blog.url_name}/"
            end
            flash[:notice]="Facebook connection created!"
            redirect "/#{@blog.url_name}/"
          else
            flash[:error]="There was a problem saving Facebook connection"
            redirect "/#{@blog.url_name}/"
          end
        else
          flash[:error]="There was a problem making Facebook connection"
          redirect "/#{@blog.url_name}/"
        end
      else
        flash[:error]="There was a problem connecting to Facebook"
        redirect "/#{@blog.url_name}/"
      end
    end

Where ##CLIENT ID## = your Application ID (mine is a 12 digit numeric value) and ## CLIENT SECRET ## = your Application Secret (mine is a 32 digit hex value).

Once you have an access_token you should be able to make calls to URLs like this:
"https://graph.facebook.com/me/?access_token=#{access_token}". The /me path is the connected user’s data and I’m grabbing their Facebook ID from the returned JSON for use elsewhere.

OAuth summarized

Application Scope

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# create the consumer...
consumer ||= OAuth::Consumer.new(KEY, SECRET, {:site => SITE, :authorize_path => PATH })

Session Scope

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# create the request token...
rt=consumer.get_request_token({ :oauth_callback => OAUTH_CALLBACK_URL })
# save the request token and secret in the session...
session[:r_token]=rt.token
session[:r_secret]=rt.secret

User Scope (Model)

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# use session values to create the request token...
rt=OAuth::RequestToken.new(consumer, session[:r_token], session[:r_secret])
# grab the user data from the OAuth provider...
access_token=rt.get_access_token({:oauth_verifier=>params[:oauth_verifier]})
oauth_user_json=access_token.get(VERIFY_PATH).body
oauth_user=JSON.parse(oauth_user_json)
# create or find the the user (using twitter.com for the email address - could use some work)... 
u=TwitterUser.first_or_create(:email=>"#{oauth_user['screen_name']}@twitter.com")
u.username=oauth_user['screen_name']
u.save!
u.oauth_tokens.all.destroy
u.oauth_tokens.new(:user_access_token=>access_token.to_yaml)
u.save!
# set the session user for future use...
session[:user]=u.id
...
# and when you need access to the OAuth provider again, use the access_token stored in the User model
u=User.first(:id=>session[:user])
access_token=YAML::load(u.oauth_tokens.first.user_access_token)
verify=access_token.get(OAUTH_PROVIDERS["https://twitter.com"][:verify_path]).body

My war is winding down with OAuth

Summary of what’s going on with OAuth:

1. create a OAuth consumer. Consumer is made up of:
   • application key
   • application secret
   • the url and path to the OAuth provider
2. create a request token:
   • this makes a call to the provider
   • the request token sends the callback URL to the provider
   • it seems like this expires pretty quickly (at least with Twitter)
   • therefore, I’ll probably hold this in a session
   • once returned from the provider, you can redirect to the provider to complete the access
   • once access is granted, the provider will return the user to the callback URL you sent
3. create the access token:
   • this makes a call to the provider
   • the user is redirected from the provider to the callback URL
   • a querystring variable – oauth_verifier – is included with the callback URL
   • the oauth_verifier value is then sent back to the provider
   • the provider then returns an access token
   • the access token can hang around for a while and I’ll save that in the database attached to the User model