Secure Webservices
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This document discusses using OAuth for securing web services on Android applications. It begins with an introduction to OAuth and its goals of allowing users to grant access to private resources like social media profiles without sharing usernames and passwords. It then explains the basic OAuth workflow involving a 3-step handshake to obtain a request token, having the user authorize the client, and exchanging the request token for an access token. The document concludes by demonstrating how to implement OAuth in an Android app using the Signpost library, which integrates with HTTP clients and handles token management.
![What is OAuth?
OAuth.net
”An open protocol to allow secure API authorization
in a simple and standard method from desktop and
web applications.”
Wikipedia.org
”OAuth is an open protocol that allows users to share
their private resources [...] stored on one site with
another site without having to hand out their
username and password.”](https://image.slidesharecdn.com/securewebservices-13008976390193-phpapp02/85/Secure-Webservices-8-320.jpg)
Secure Webservices
- 1. Secure Web Services with OAuth ~ Matthias Käppler ~ February 23rd, 2010
- 2. Outline 1) Who Am I 2) Motivation 3) Introduction to OAuth 4) How OAuth works 5) OAuth on Android with Signpost
- 3. Europe's leading local review site 17M uniques I'm the Android guy at Qype.com!
- 4. The mobile Web What was WAP again? Nevermind. With today's hardware and infrastructure, mobile applications have become full blown Web clients.
- 5. Mobile HTTP Clients Secure channel? Data integrity? Client Web service Authentication? Authorized access?
- 6. HTTPS Secure Socket Layer + HTTP Secures the whole communication channel Uses certificates and public key encryption Very secure! But...
- 7. Right tool for the job? Does all my data need encryption? Do users know, care about, or trust digital certificates? I'm still giving away my password! What about authorization, and who actually decides that?
- 8. What is OAuth? OAuth.net ”An open protocol to allow secure API authorization in a simple and standard method from desktop and web applications.” Wikipedia.org ”OAuth is an open protocol that allows users to share their private resources [...] stored on one site with another site without having to hand out their username and password.”
- 9. Motivation Web users typically have their data spread across various, often interweaved websites e.g. Flickr, Twitter, Vimeo, ... Each time users want to access their data, they must give away their username and password
- 10. Motivation Now imagine you would do that with your credit card!
- 11. Where OAuth sets in Without OAuth, users have to share their credentials with potentially untrustworthy applications. a.k.a. the ”password anti-pattern” OAuth solves this by letting the user grant revokable access rights over a limited period of time.
- 12. Implications OAuth does not require the user to trust the client application. instead: OAuth is about trust into the service being used.
- 13. Implications OAuth does not automatically grant clients permission by e.g. issueing certificates. instead: OAuth is about access right delegation from user to client.
- 14. How OAuth works Ever heard of... They use OAuth!
- 15. How OAuth works Alice wants to read her latest mentions on her Android phone using SecTweet. Or in OAuth lingo: Consumer SecTweet requires user Alice's permission to access the protected resource http://twitter.com/statuses/mentions from the service provider Twitter.
- 16. OAuth Access Delegation SecTweet does not yet have Alice's permission to access Twitter mentions on her behalf. However, Alice can pass authorization over to SecTweet by means of an access token. As long as this token is valid, SecTweet is allowed to access Alice's resources.
- 17. OAuth Access Delegation This is done by doing the OAuth dance. 3-way handshake
- 18. Step 1: The request token GET twitter.com/oauth/request_token SecTweet request token SecTweet contacts twitter.com, asking for a request token. This token must be ”blessed” by Alice.
- 19. Step 2: Token blessing open web browser / web view SecTweet call back with token + verification code SecTweet opens Twitter's authorization website in a browser (or Web view). Alice is asked to either grant or deny SecTweet access to her Twitter data.
- 20. Step 2: Token blessing
- 21. Step 3: Token exchange GET twitter.com/oauth/access_token SecTweet access token If Alice agrees, SecTweet will then exchange the blessed request token for an access token.
- 22. Message signing Once an access token has been retrieved, SecTweet can use it to access Alice's resources on Twitter.com by signing all requests with it. HTTP message Signature
- 23. Message Signing There is no need to store Alice's username or password on the device.
- 24. Message Signing An OAuth signature is a unique fingerprint, typically computed using keyed cryptographic hash functions. Thus, both integrity and authenticity of a signed message can be verified by the receiver. Signatures are protected from eavesdropping and replay attacks by using timestamps and nonces.
- 25. Example GET /statuses/mentions.xml HTTP/1.1 Host: twitter.com Authorization: OAuth oauth_version='1.0', oauth_consumer_key='v5Dev9QtVuzkhssYoH', oauth_token='pbZXhbz2p5w8h6y', oauth_timestamp='1265563431', oauth_nonce='73980654659', oauth_signature='pvISiky7dm9FD45mfZkP0S50yu0=', oauth_signature_method='HMAC-SHA1'
- 26. Observations so far OAuth is not just about machines. It actually involves the user as an authority. OAuth protects the user's credentials by simply not sending them! OAuth checks the integrity, authenticity and authorization of Web service calls.
- 27. Observations so far OAuth operates on the same OSI layer as HTTP and integrates seamlessly with it. OAuth does not obfuscate message payload, making it easy to debug. OAuth itself is a fairly non-technical protocol. It emerged from real world requirements and use cases.
- 28. On the flip-side OAuth requires a fair amount of set-up work, e.g. for keeping track of nonces and tokens. OAuth affects the user signup journey. Balancing UX here can be a two-edged sword.
- 29. On the flip-side OAuth does not guarantee data privacy. It must be used in conjunction with existing protocols to achieve that (e.g. SSL). The OAuth standard is unclear and difficult to read at times, resulting in compatibility issues. Hammer time!
- 30. OAuth on Android What we need is a library which is: Written in Java. Integrates with Apache Commons HTTP. Is lightweight and easy to integrate.
- 31. That would be Signpost Signpost is an extensible, HTTP layer independent, client-side OAuth library for the Java platform. It works on Android!
- 32. Using Signpost Have an Activity that can receive callbacks: <activity android:name=".activities.OAuthActivity"> <intent-filter> <action android:name="android.intent.action.VIEW" /> <category android:name="android.intent.category.DEFAULT"/> <category android:name="android.intent.category.BROWSABLE"/> <data android:scheme="mycallback"/> </intent-filter> </activity>
- 33. Using Signpost Implement OAuthActivity to have a Signpost OAuthConsumer and OAuthProvider: public class OAuthActivity { private OAuthConsumer consumer = new CommonsHttpOAuthConsumer(CONSUMER_KEY, CONSUMER_SECRET); private OAuthProvider provider = new CommonsHttpOAuthProvider( 'http://example.com/oauth/request_token', 'http://example.com/oauth/access_token', 'http://www.example.com/oauth/authorize'); . . . }
- 34. Using Signpost Step 1: Retrieving the request token public class OAuthActivity { private void step1() { String url = provider.retrieveRequestToken(consumer, 'mycallback:///'); storeTokenToPreferences(consumer.getToken()); storeTokenSecretToPreferences(consumer.getTokenSecret()); startActivity(new Intent(Intent.ACTION_VIEW, Uri.parse(url)); } }
- 35. Step 2: Token blessing
- 36. Using Signpost Step 3: Retrieving the access token public class OAuthActivity { // website called back with: // mycallback:///?oauth_token=xxx&oauth_verifier=12345 private void step3(callbackUrl) { String oauthVerifier = callbackUrl.getQueryParameter(OAuth.OAUTH_VERIFIER); String token = readTokenFromPreferences(); String secret = readSecretFromPreferences(); provider.retrieveAccessToken(consumer, oauthVerifier); storeTokenToPreferences(consumer.getToken()); storeTokenSecretToPreferences(consumer.getTokenSecret()); } }
- 37. Using Signpost Signing messages sent with HttpClient: public class AnyActivity { private HttpClient httpClient = new DefaultHttpClient(); private void sendSignedRequest() { HttpRequest request = new HttpGet('http://example.com/protected.xml'); consumer.sign(request); HttpResponse response = httpClient.execute(request); // . . . } }
- 38. Outlook: WRAP The Web Resource Authorization Protocol is an OAuth variant, aiming to simplify and extend OAuth 1.0a Drops signatures in favor of SSL secured connections and short lived access-tokens Defines additional ways to retrieve tokens
- 39. More information oauth.net hueniverse.com/oauth
- 40. More information code.google.com/p/oauth-signpost
- 41. Get involved $ git clone git://github.com/kaeppler/signpost.git
- 42. Thank you