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Kirsten Jones, Technical Leader, Cisco Systems

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1 Kirsten Jones, Technical Leader, Cisco Systems
Demystifying REST

2 Who’s this talk for? Application Developers …Curious about using REST
…Wanting help debugging the system Not REST API Architects (sorry!)

3 What Will I Cover? HTTP Overview REST Web Services
OAuth Authentication Basics REST Debugging

4 HTTP – Protocol for the Web
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

5 How does HTTP Work? Client sends a request
Method URL Headers (sometimes) parameters (sometimes) body Server replies with a response Content Status

6 What do you Mean, Status? HTTP response codes for dummies.
50x: we fucked up. 40x: you fucked up. 30x: ask that dude over there. 20x: cool. Props for this

7 Headers vs. Parameters Headers Parameters
Generally meta-information about the request For instance: requesting an image in a specific format Parameters Limit or describe how you want the resource (searches, filters) Defines the resource you’re requesting

8 Request and Response Headers
Request (client) Accept: Give me this kind of response. Here’s a list in order of what I’m hoping you’ll send. Accept: text/html,application/xhtml+xml,application/xml Response (server) Content-Type: This is the kind of response I’m sending you. Content-Type: text/html; charset=UTF-8

9 Parameters Part of the URL
Everything after the question mark, delimited by ampersands

10 An example request Chrome browser sends a request to Google
Method: GET URL: 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 ,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/ (KHTML, like Gecko) Chrome/ 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= :LM= :S=W0Hha7x4czdXp51U Host:

11 Example Response 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 :26:46 GMT; path=/;; 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 :26:46 GMT Content: A bunch of HTML Status: 200

12 Watching HTTP traffic Some browsers provide tools to view HTTP traffic
Great for understanding what your browser is doing Tracking programmatic traffic requires a separate tool

13 HTTP Sniffers Macintosh: HTTPScoop
Macintosh: Charles (supports SSL) Windows: Fiddler Unix (or Mac): Wireshark (X11)

14 Example: HTTPScoop

15 Example: HTTPScoop Request

16 Example: HTTPScoop Headers

17 Example: HTTPScoop Request/Response

18 REST APIs Leverage HTTP
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

19 Example REST Request Blog Info from Tumblr
GET (read) Requires api_key sent as parameter

20 Example Request: Httpscoop

21 Example Request: Httpscoop

22 Example Request: Httpscoop

23 Example REST Response Status: 200 Content: {"meta": {"status":200, "msg":"OK” }, "response":{ "blog":{"title":"Untitled","posts":0, "name":"synedra", "url":"http:\/\/\/", "updated":0, "description":"","ask":false,"likes":0}}}

24 OAuth Authentication 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

25 How does OAuth Work? 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

26 OAuth Example - Parameters
Signature is generated based on URL Parameters Consumer key User token

27 OAuth Example - Parameters

28 OAuth Example - Parameters
Headers (nothing special)

29 OAuth Example - Parameters

30 OAuth Example - Header Signature is generated based on
URL Parameters Consumer key User token URL is unchanged: Authorization header has oauth stuff: OAuth realm="", oauth_body_hash="JtgCKBurLIPLM4dXkn2E3lgrfI4%3D", oauth_nonce=" ", oauth_timestamp=" ", oauth_consumer_key=”***KEY***", oauth_signature_method="HMAC-SHA1", oauth_version="1.0", oauth_token=”***TOKEN***", oauth_signature="8iWVpIK3LhRbu8JPf2gzC1YxQy4%3D"

31 OAuth Example - Header No authorization parameters

32 OAuth Example - Header Authorization is in the header

33 OAuth Example - Header Request/response works the same

34 Using OAuth with Python
Download the oauth2 package from github No, it’s OAuth 1.0a, ignore the name Quick walkthrough to understand process (but this talk is not about OAuth) import oauth2 as oauth consumer_key = 'xxxxxxxxxxxxxx' consumer_secret = 'xxxxxxxxxxxxxx’ consumer = oauth.Consumer(consumer_key, consumer_secret) client = oauth.Client(consumer)

35 Get a request token First step in OAuth: Get a request token for this authorization session OAuth library handles signing the request import oauth2 as oauth consumer_key = 'xxxxxxxxxxxxxx' consumer_secret = 'xxxxxxxxxxxxxx’ consumer = oauth.Consumer(consumer_key, consumer_secret) client = oauth.Client(consumer) resp, content = client.request(request_token_url, "POST") request_token = dict(urlparse.parse_qsl(content))

36 Get a verifier 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 print "Go to the following link in your browser:" print "%s?oauth_token=%s" % (authorize_url, request_token['oauth_token']) accepted = 'n' while accepted.lower() == 'n': accepted = raw_input('Have you authorized me? (y/n) ') oauth_verifier = raw_input('What is the PIN? ’)

37 Get the access token Third step: Use the verifier and the request token to get an access token This is usually a long lived token token = oauth.Token(request_token['oauth_token'], request_token['oauth_token_secret']) token.set_verifier(oauth_verifier) client = oauth.Client(consumer, token) resp, content = client.request(access_token_url, "POST") access_token = dict(urlparse.parse_qsl(content))

38 Make a call Make an API call using the OAuth library
The library handles the signature generation url = consumer = oauth.Consumer( key=”XXXXX", secret=”XXXXX") token = oauth.Token( client = oauth.Client(consumer, token) resp, content = client.request(url)

39 Debugging APIs Use the documentation and resources provided by the platform team Consoles, IODocs, OAuth signature checkers Use existing, tested libraries Code defensively

40 Common Errors 401 authentication errors (signatures, tokens)
403 authorization errors (throttles, permissions) 400 errors – parameters, headers Library out of sync with API

41 Debugging Strategies Try building the request using just the OAuth library Find someone else’s code that works HTTP Servers aren’t that smart

42 Summary HTTP: Hypertext Transfer Protocol
REST: REpresentational State Transfer OAuth: Authentication

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