DEMYSTIFYING REST Kirsten Jones REST web services are everywhere! It seems like everything you want is available via a web service, but getting started with one of these web services can be overwhelming – and debugging the interactions bewilders some of the smartest developers I know. In this talk, I will talk about HTTP, how it works, and how to watch and understand the traffic between your system and the server. From there I’ll proceed to REST – how REST web services layer on top of HTTP and how you can expect a REST web service to behave. We’ll go over how to monitor and understand requests and responses for these services. Once we’ve covered that, I’ll talk about how OAuth is used for authentication in the framework of a REST application. PHP code samples will be shown for interacting with an OAuth REST web service, and I will cover http monitoring tools for multiple OS’s. When you’re done with this talk you’ll understand enough about REST web services to be able to get started confidently, and debug many of the common issues you may encounter.

1. Kirsten Jones, Technical Leader, Cisco Systems

2.  HTTP Overview
 REST Web Services
 OAuth Authentication

3.  HyperText Transfer Protocol
 Used for conversations between web clients
and servers
 Most of the internet uses HTTP
 Supports verbs for GET, PUT, POST, DELETE
 Query parameter framework

4.  Client sends a request
 Method
 URL
 Headers
 (sometimes) parameters
 (sometimes) body
 Server replies with a response
 Content
 Status
 Headers

5. HTTP response codes for dummies.
 50x: we fucked up.
 40x: you fucked up.
 30x: ask that dude over there.
 20x: cool.
Props to @DanaDanger for that one

6.  Chrome browser sends a request to Google
 Method: GET
 URL: http://www.google.com
 Headers:
▪ Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8
▪ Accept-Language: en-US,en;q=0.8
▪ Accept-Charset: ISO-8859-1,utf-8;q=0.7,*;q=0.3
▪ Connection: keep-alive
▪ User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_7_3)
AppleWebKit/535.19 (KHTML, like Gecko) Chrome/18.0.1025.168 Safari/535.19
▪ Accept-Encoding: gzip,deflate,sdch
▪ Cookie: NID=59=EudJ2a15ql8832PCysQA0qchtuvGWMoA7rkp79VpIYAQ8-
j42IO17LFudCYNMXm9l6SHcu3YgrGRCdrRCyM468xPZaOek4Pi-
AXQ8eARqU1SGYx6y7_9LW-c3HHb-vs2;
PREF=ID=994f8de0e8b39a5b:U=237805f1f710dc73:FF=0:TM=1336752507:LM=13
36752509:S=W0Hha7x4czdXp51U
▪ Host: www.google.com

7.  Google sends a response
 Headers:
▪ Content-Length: 24716
▪ Content-Encoding: gzip
▪ Set-Cookie: NID=59=F48kbwfwOi-qCHJyrnMSUlDBVxK-
ZVKZpq5B5jttt_25IRN4lS-0rQcVttq-
dnOIlQzafw1i4HPQAO0RpZ7NuC0WCKWta7SYoekx0--YGf2zIFZ9VXIKS-
_UEaOH9iBe; expires=Sat, 10-Nov-2012 21:26:46 GMT; path=/;
domain=.google.com; HttpOnly
▪ Expires: -1
▪ Server: gws
▪ X-XSS-Protection: 1; mode=block
▪ Cache-Control: private, max-age=0
▪ X-Frame-Options: SAMEORIGIN
▪ Content-Type: text/html; charset=UTF-8
▪ Date: Fri, 11 May 2012 21:26:46 GMT
 Content: A bunch of HTML
 Status: 200

8.  Macintosh: HTTPScoop
http://tuffcode.com/
 Macintosh: Charles (supports SSL)
http://www.charlesproxy.com/
 Windows: Fiddler
http://www.fiddler2.com/fiddler2/
 Unix (or Mac): Wireshark (X11)
http://www.wireshark.org/

9. Request

10. Headers

11. Request/Response

12.  Uses URL paths to define resources
 Create, Read, Update, Delete
 POST, GET, PUT, DELETE
 Error Codes
 HTTP Status Codes
 Request parameters
 Query parameters
 Response types and configuration
 Headers

13.  Blog Info from Tumblr
 GET (read)
http://api.tumblr.com/v2/blog/synedra.tumbl
er.com/info
 Requires api_key sent as parameter

15.  Headers

16.  Request/Response

17. Status: 200
Content:
{"meta":
{"status":200, "msg":"OK” },
"response":{
"blog":{"title":"Untitled","posts":0,
"name":"synedra",
"url":"http://synedra.tumblr.com/",
"updated":0,
"description":"","ask":false,"likes":0}}}

18.  Monitor application use
 Know which users are making requests
 Prevent DDOS attacks on the system

19.  Used by many APIs
 Each application gets a consumer key and secret
 Authentication server handles authentication
 Each user of an application gets a unique user
token and secret
 Supports tracking of application/member use of
the API
 Allows users to protect username/password
 Industry standard – libraries for most
programming languages

20.  REST web services call adds verification
signature to each request
 Query parameters
 Authorization header
 Secrets are used to create signature
 Authentication server checks signature to
verify that it was created using shared secrets
 If authentication succeeds, request is
processed by API server

21.  Signature is generated based on
 URL
 Parameters
 Consumer key
 User token
 http://api.linkedin.com/v1/people/url=http%3A%2F%2Fw
ww.linkedin.com%2Fin%2Fsynedra?oauth_body_hash=2j
mj7l5rSw0yVb%2FvlWAYkK%2FYBwk%3D&oauth_nonce
=6283929&oauth_timestamp=1336775605&oauth_consu
mer_key=***KEY***&oauth_signature_method=HMAC-
SHA1&oauth_version=1.0&oauth_token=***TOKEN***
&oauth_signature=CqHiZI6tI3pQGe5a0vVgoT0822A%3D

22.  Request

23.  Headers (nothing special)

24.  Request/Response

25.  Signature is generated based on
 URL
 Parameters
 Consumer key
 User token
 URL is unchanged:
http://api.linkedin.com/v1/people/~/shares
 Authorization header has oauth stuff:
OAuth realm="http://api.linkedin.com",
oauth_body_hash="JtgCKBurLIPLM4dXkn2E3lgrfI4%3D",
oauth_nonce="60723468", oauth_timestamp="1336776657",
oauth_consumer_key=”***KEY***",
oauth_signature_method="HMAC-SHA1", oauth_version="1.0",
oauth_token=”***TOKEN***",
oauth_signature="8iWVpIK3LhRbu8JPf2gzC1YxQy4%3D"

26.  No authorization parameters

27.  Authorization is in the header

28.  Request/response works the same

29.  How to use PECL OAuth to sign API requests
 http://pecl.php.net/package/oauth
 Quick walkthrough to understand process
(but this talk is not about Oauth)

30.  First step in OAuth: Get a request token for
this authorization session
 OAuth library handles signing the request

31.  Second step: Send the user to the server to
authorize your application
 After the user authorizes your
application, the server returns a verification
code for you to use

32.  Third step: Use the verifier and the request
token to get an access token
 This is a long lived token

33.  Make an API call using the OAuth library
 The library handles the signature generation

34.  HTTP: Hypertext Transfer Protocol
 REST: REpresentational State Transfer
 OAuth: Authentication