Wednesday, July 3, 2013

Integrating Twitter 1.1 api in Android with oauth including app-only authentication

Introduction

One major change is that all API calls now have to be authenticated (and authorized) via OAuth: "user authorization (and access tokens) are required for all API 1.1 requests". That means any action on Twitter that is related to a user has to happen this way.

Luckily there is also a so called application-only (app-only) authentication for actions that don't require a user as a context. Those are requests on behalf of an application. Think about search and getting a timeline for a user. One thing that's definitely different from the other calls is that this app-only authentication has to use OAuth 2.0, while the user-context based authentication has to use OAuth 1.0a!

In this post I'll describe how to implement both, including a full working Android code example.




App-only Twitter 1.1 Authentication OAuth 2.0

Information about this principle can be found here. As said above, you can use it for accessing the Twitter API 1.1 endpoints that do not require a user action. For example searching for tweets falls in this category; just like getting a tweet from a user's timeline. Tweeting a status update does not fall in this category, because a user has to give permission for this. You can see if a Twitter API call supports application-only authentication if there's a rate-limit specified with it. E.g for the search it says on the right: 450/app. So that's accessible via the app-only API. But getting a user's direct messages isn't, it only has 15/user specified.

The problem with this userless-context API solution I had was my app was using the Signpost library for the Twitter 1.0 API. I preferably would have used that lib for this app-only authentication too, but the Signpost still does not support OAuth 2 yet...
Then I tried to use the Scribe library, which supports OAuth 2.0, but I couldn't get that working quickly. 
Therefore I went back to the basics and used plain HTTP POST and GET methods, using this blogpost as a starting point. All pieces to get it working are in that post, but not available as one complete code set, that's why I made this post. Plus you might come along a few problems too... also described below.

Making it work

Easiest is to refer to the above mentioned Crazy Bob's blogpost to get started and what's happening why.
In my attached example code (see bottom of this post) most of the logic occurs in OAuthTwitterClient.java. In OnCreate() the UI is set up, including the consumer, provider and client for the OAuth 1.0a using Signpost (see next section for details on that part).

When a user clicks on the top button of the application, named '1a) Request bearer-token via app-only oauth2') the getBearerTokenOnClickListener.onClick() method is invoked. There you see the bearer token getting retrieved via requestBearerToken(), as described in Crazy Bob's blogpost.
That should give the bearer token which you need as mentioned here
Then to get a tweet from a Twitter user (in the code I'm using 'twitterapi'), click on the second button named '1b) Get tweet from user via app-only oauth2'. That invokes its listener which invokes fetchTimelineTweet(), which in turn gets the tweet using the bearer token, after which the tweet is displayed on the screen.

Troubleshooting 

I ran into a few issues:
  1. When fetching the tweet, the getInputStream (in readResponse()) was giving a FileNotFoundException. Turns out that since Android 4 ICS (Ice Cream Sandwich), this can occur because the conn.setDoOutput(true) causes the request to be turned into a POST even though the specified request method is GET! See here. The fix is to remove that line.
  2. When invoking requestBearerToken() two times in a row on Android 1.5, the responseCode showed as -1 sometimes; mainly when waiting about 30 seconds before invoking it again. That turned out to be a known issue for Android before 2.2 Froyo. For that the method disableConnectionReuseIfNecessary() is put in place. 
  3. It seems a bearer token lasts "forever", until it is revoked/invalidated. Twitter can do that but you can do it yourself too, via the invalidate_token API call.
PS 1: no the code is not optimal, for example the error handling can be done a lot better
PS 2: and no the UI won't win any "Best Interface" prizes
PS 3: yes all network calls should be done on a non-UI thread really. Yup that's some homework for you too :)


User Context Twitter 1.1 Authentication OAuth 1.0a

For updating a user's status (i.e. tweeting), you have to be authenticated and the user has to have authorized you to perform those type of actions. Usually the user authorization happens by switching to a browser in which the user has to log in to Twitter and say whether the application is allowed to perform the requested actions.
Luckily, for this type of authentication still the Signpost library can be used since its based on OAuth 1.0a.

Making it work

After upgrading to the signpost-core-1.2.1.2.jar and signpost-commonshttp4-1.2.1.2.jars, everything almost worked immediately. Especially make sure to use CommonsHttpOAuthProvider as it says on the Signpost homepage in the Android section.

Since my app still runs on Android SDK 1.5 (yes!) I tested the solution on a 1.5 emulator.
But then I ran into my first problem, authentication failed with: javax.net.ssl.SSLException: Not trusted server certificate.
To get this working, I had to make sure all the Twitter Root CA certificates are known. For that I used this blogpost. See the class CrazyBobHttpClient for the implementation. After putting in all VeriSign certificates one by one (search for the string 'class 3 Public Primary Certification Authority - G' in the .pem file mentioned in this Twitter Developers Forum post to find all 5 of them).
In short, issue the following command to have each one added to your own keystore:

C:\>C:\jdk1.7.0_17\jre\bin\keytool -import -v -trustcacerts -alias 3 -file verisign_cert_class3_g5.cert -keystore twitterkeystore.bks -storetype BKS -provider org.bouncycastle.jce.provider.BouncyCastleProvider -providerpath bcprov-jdk16-145.jar -storepass ez24get

So in the above I'm adding the VeriSign G5 certificate. The -alias 3 you have to increase each time. And notice the password used: 'ez24get', you'll find that in the CrazyBobHttpClient class.

If you see:

Certificate already exists in system-wide CA keystore under alias
Do you still want to add it to your own keystore? [no]:  

answer with: yes

And do the same for the DigiCert certificates, you only need the 3 Root ones. You can find the separate certificates and keystore in the res/raw directory of the example application. The separate certificates don't have to be provided, I just left them there for reference.

After performing all these steps, I was able to authenticate and even tweet. Just as a test I switched back to the DefaultHttpClient(). And the authentication now goes fine using that implementation too! Strange, because AFAIK that one just uses the default system keystore, and before it gave the "not trusted server certificate error"... Strange to me. If anybody knows the reason why, please leave it in the comments!

PS: maybe even cleaner is to add your own created keystore to the existing keystore(s). See the comments at the top in the CrazyBobHttpClient.java.


Outstanding Issues

Well, issues.... more like questions: 
  • Why does the DefaultHttpClient() suddenly work (see previous section)?
  • It would be nice to have an example for app-only authentication using an OAuth 2.0 library like Scribe instead of using this low level POST/GET code.
  • In the LogCat I see these messages appear after each API call:

    07-01 18:59:03.575: W/ResponseProcessCookies(732): Invalid cookie header: "set-cookie: guest_id=v1%3A137270514572832152;  Domain=.twitter.com; Path=/; Expires=Wed, 01-Jul-2015 18:59:05 UTC". Unable to parse expires attribute: Wed, 01-Jul-2015 18:59:05 UTC
    Why do these appear?
  • It should be possible to get the Twitter Timeline for a given user using your application's private access tokens (and thus not requiring the app-only authentication). Of course this is not recommended, because that would mean you'd have to put these tokens in your application. But for some situations it could be an option. See this PHP code on how that can be done.


The Sample Code Application

You can find the complete source code here
It should run on anything from Android 1.5 and higher.
It has been tested by me on:
  • Android 1.5 emulator
  • Android 4.0 Samsung S2
  • Android 4.0 emulator
You might want to remove the scribe-oauth2.0-1.3.0.jar from the libs directory, just left it there for reference. Same goes for the certificates in the res/raw/ directory. Removal is not necessary, it just uses unnecssary storage.

How to run it

  1. Load the project in your favorite IDE or whatever you use to build Android applications.
  2. In OAuthTwitterClient change the values of CONSUMER_KEY and CONSUMER_SECRET to your own application keys.
  3. Also modify the CALLBACK_URL to your application's callback URL. Note: you can also make an OOB (out-of-bounds) call that doesn't require a callback URL, but that's for you to figure out, didn't spend time on that.
  4. Deploy it. You should see a screen like this:


  5. Press button 1a) to get a bearer token. After pressing it should look like:


  6. Press 1b) to get the tweet. That should look like:


  7. Press button 2a) to get authenticated and authorized to post a tweet on behalf of a user. When the browser opens, enter the credentials under which account the tweet should be performed (no screenshot for that one). Then authorize the app (click Authorize app):




    It should get back to:




    Note: I am getting a message that the certificate is not ok. This is I think because the quite old 1.5 emulator does not have that root certificate:




    Because the certificate looks fine: 
  8. Enter a tweet text.
  9. Press button 2b) to tweet the text above it. That should give you:


  10. At the bottom of the screen you can see some statuses of what's going on. If you see any error message, check the LogCat.
  11. That's it!
And here two examples of what it can look like after integration in an app, here in the free Android SongDNA app.
Showing all tweets with the words 'shakira' and 'underneath your clothes' in it.



And the different actions possible on each tweet:



6 comments:

Ashwini J A said...

Hi TECHIE,

I have downloaded your whole code and tried to run the application. But I end up with errors.Please help me to solve this.
following error I got-
07-19 18:01:06.549: W/DefaultRequestDirector(13553): Authentication error: Unable to respond to any of these challenges: {}
07-19 18:01:06.549: E/(13553): TwitterConnector failed, statusCode not 200 but 401, reason = Unauthorized
07-19 18:01:06.564: E/(13553): Unable to post tweet update, exception =
07-19 18:01:06.564: E/(13553): oauth.signpost.exception.OAuthNotAuthorizedException: Authorization failed (server replied with a 401). This can happen if the consumer key was not correct or the signatures did not match.
07-19 18:01:06.564: E/(13553): at com.example.twitterclientoauth.OAuthTwitterClient$2.onClick(OAuthTwitterClient.java:186)

Techie said...

Hi Ashwini, looks like you're trying to send a tweet (status update). And it fails because you're not authorized. Did you successfully go through step 7, where button 2a) is pressed so the app gets authorized on behalf of a twitter user?

So first make sure after pressing button 2a), after the 'Result:' at the bottom of the screen it should say "Authorized!!"; see the 2nd screenshot in step 7. If it didn't then you also can't post a tweet because the app is not authorized to do so on behalf of that/a user (see first image in step 7). Check the logcat output for more details on why the authorization failed.

If you did get the "Authorized!!" message (but I doubt that :), then there's something else wrong, but I need more from the logcat to figure it out.

Shefa said...

Hi Techie , I tried to open the link where you have provided the source code, unfortunately it's not opening. It is saying "Web Page is not available"

Techie said...

@Shefa: weird, I just tried it and it works. Try copying the link into your browser, just tried that too and it worked for me. (and also worked for the person of the first comment, so should be fine :)

Anonymous said...

Hii techie what to put in callback url to get back to activity after authorising app while login

Techie said...

@anonymous: an example would be String CALLBACK_URL = "songdna://twitter". The 'songdna' part should be replaced, with your own app name for example.