OAuth
Practical Implementation

Pownce and OAuth
• Pownce launched (June 2007)
• developers wanted an API
• became involved with OAuth (Aug 2007)
• public read-only API (Oct 2007)
• full API with OAuth (Mar 2008)
• 200+ apps built on Pownce API

Me and OAuth
• an author of the specification
• wrote first library (Python)
• maintain Python library
• maintain Pownce API OAuth implementation

What is OAuth?
A simple open standard for secure API
authentication.
http://oauth.net

The (API) Love Triangle
End User
Web Service 3rd Party App
“Service Provider” “Consumer Application”
Pownce AIM bot

Specifically OAuth is...
• Authentication
Need to log in to access parts of a website
ex: bookmark a link, post a photo, add a friend, view
a private message
• Token-based Authentication
Logged-in user has a unique token used to access
data from the site

Just like...
• Flickr Auth
• Google’s AuthSub
• Yahoo’s BBAuth
• Facebook Auth
• and others...
http://flickr.com/photos/bees/2504039638/

Who is involved?

Who is it for?
• Serviceauthorizationhavecertain functions
Providers - an web API that
needs for
• Consumers -encourages) OAuth that
want to use an API
requires (or

Goals:
Be Simple
• standard for website API authentication
• consistent for developers
• easy for end users to understand *
* this is hard

Goals:
Be Secure
• secure for end users
• easy to implement security features for
website developers
• 3rd party developers don’t have access to
passwords
• balance security with ease of use

Goals:
Be Open
• any website can implement OAuth
• any 3rd party developer can use OAuth
• open source client libraries
• community-designed technical specifications

Goals:
Be Flexible
• authentication method agnostic
• users don’t need a username and password
• can use OpenID (or not!)
• whatever auth works best for the service
• 3rd party developers don’t handle auth

Is OAuth different from
OpenID?
Yes.
(short answer)

Is OAuth different from
OpenID?
OpenID - user identification by provider
URL, login on provider site.
OAuth - API authorization and permissions,
any form of user identification, login on
provider site.
(medium answer)

Is OAuth different from
OpenID?
http://www.pointy-stick.com/blog/2008/03/13/
explanation-difference-between-openid-and-oauth/
(long answer)

What the end user sees...
Web Consumer
Ma.gnolia and Nsyght
I’d like to search my Ma.gnolia
bookmarks via social search
engine Nsyght.

OMG! Need to log in!

Login with service provider
service provider’s site!
alternative login method
not username/password

Authorize

Done!

Web flow
Request Token!
Nsyght Ma.gnolia
API calls
asks for
request token
returns
request token
...

Authorize!
user sent http redirect
to ma.gnolia with
request token in
URL user logs in
and/or authorizes
nsyght
redirected back
...
to nsyght
with (authorized)
...
request token
Nsyght Ma.gnolia

Access Token!
ask for access API calls
token with
authorized request token
request token exchanged for
access token
nsyght stores
access token
Nsyght Ma.gnolia

use the access token...
by Blaine Cook

What the end user sees...
Desktop Consumer
Pownce and PownceAIM
I’d like to get alerts about new
Pownce notes via AIM.

OMG! Need to log in!

Login with service provider
service provider’s site!

Authorize
click “Okay!”

Authorized!
Return to
desktop app.

Desktop flow
Request Token!
PownceAIM Pownce
API calls
asks for
request token
returns
request token
...

Authorize!
user sent user follows link
to Pownce with
request token in
URL user logs in
and/or authorizes
PownceAIM
user tells
...
PownceAIM
that auth is
...
complete
PownceAIM Pownce

Access Token!
ask for access API calls
token with
authorized request token
request token exchanged for
access token
PownceAIM stores
access token
PownceAIM Pownce

Basic Authorization Process
1. Obtain request token
2. User authorizes
request token
3. Exchange request token
for access token
4. Use access token to
obtain protected resources

OAuth Setup
• Service provider gives documentation of
authorization URLs and methods
• Consumer registers an application with the
service provider

Service Provider
Documentation
• Request token endpoint
• Authorization endpoint
• Access token endpoint
• Accepted request method(s) (GET, POST,
PUT, etc...)
• Signature method(s)
• Extra parameters (non-oauth)
• Any specific notes about OAuth for that
provider

Pownce API Documentation
https://pownce.pbwiki.com/API%20Documentation2-0#VerifyAuth

Register a Consumer
Application
• Consumer gives service provider data
about the application (name, creator, url
etc...)
• Service provider assigns the application a
consumer key and consumer secret

Registering a
Fire Eagle Application
consumer app
sign up page
https://fireeagle.yahoo.net/developer/create

Registering a Fire Eagle Application
Done!
oooh!
https://fireeagle.yahoo.net/developer/manage

OAuth Objects -
Consumer
consumer key
• assigned during consumer registration
• passed as a request parameter
consumer secret
• assigned during consumer registration
• used for signing (e.g. HMAC-SHA1)

OAuth Objects -
Consumer

OAuth Objects - Token
token key
• unique string granted by service provider
• passed as a request parameter
• same variable name (oauth_token_key) for
both request and access type tokens
token secret
• also granted by service provider
• same variable name (oauth_token_secret)
for both request and access type tokens

OAuth Objects - Token

OAuth Parameters
• oauth_consumer_key
• oauth_token
• oauth_signature
• oauth_signature_method
• oauth_timestamp
• oauth_nonce
• oauth_version

Where is this
information passed?
(in order of preference)
• HTTP Authorization header
• HTTP POST request body (form params)
• URL query string parameters

Timestamp and Nonce
oauth_timestamp
• seconds since Unix epoch (unless otherwise specified
by service provider)
• must be equal or greater than previous request
oauth_nonce
• random string per timestamp / request
• attempt to stop replay attacks

Signing Requests
oauth_signature_method
• HMAC-SHA1
• RSA-SHA1
• PLAINTEXT
oauth_signature
• string constructed according to the chosen signature
method

Signing Requests

Signature Methods
HMAC-SHA1
• construct thewith a ‘&’: base string by joining
signature
the following
1. http request method (e.g. GET)
2. http url (endpoint url)
3. normalized request parameters (sorted by
name)
• key = encoded consumer secret and token
secret separated by an ‘&’

Signature Methods
HMAC-SHA1

Signature Methods
HMAC-SHA1
Example base string:
GET
&http%3A%2F%2Fapi.pownce.com%2Fauth%2Fverify.xml
&oauth_consumer_key%3Dnbe958225r999a706d1u4qgwx2nx9e8j
%26oauth_nonce%3DD81FBEDC-1050-40EE-
B899-21A1E07C4EC5
%26oauth_signature_method%3DHMAC-SHA1
%26oauth_timestamp%3D1211254098
%26oauth_token%3D0qic7f318nj42ogm
%26oauth_version%3D1.0
Example signature:
oauth_signature=\"UFHiNYSf++3N18oTZ864IAGlvxU%3D\"

Signature Methods
PLAINTEXT
• should be used over a secure channel (SSL)
• no base string
• url-encoded consumer ‘&’ and token
secret
secret separated by an

Signature Methods
PLAINTEXT
Ex:
oauth_signature=djr9rjt0jd78jf88%26jjd999tj88uiths3

Signature Methods
RSA-SHA1
• sign signature base string private key and
with Consumer’s RSA
the
• verify with Consumer’s RSA public key
• same signature base string as HMAC-SHA1
• still in development for most OAuth libraries

Big Fatty Example
PownceAIM and Pownce
warning: screen shots might not match text.

PownceAIM Pownce
API call
asks for
request token
Authorization: OAuth realm=\"http://api.pownce.com/\",
oauth_consumer_key=\"nbe958225r999a706d1u4qgwx2nx9e8j\",
oauth_signature_method=\"HMAC-SHA1\",
oauth_signature=\"7A4blmAxXMDPmCQuTBR4CocpdNo%3D\",
oauth_timestamp=\"1211257266\",
oauth_nonce=\"9BD703ED-EBA0-4B79-B9F2-AA09C9945D4B\",
oauth_version=\"1.0\"
returns
request token
oauth_token_secret=f23dzf5l79o2q23y&oauth_token=3fjay66o4x78j4c8

PownceAIM Pownce
user follows link
user sent user logs in
to Pownce with and/or authorizes
request token in PownceAIM
URL
http://api.pownce.com/oauth/authorize?oauth_token=3fjay66o4x78j4c8

let’s pretend the user is logged in to the Pownce site
click “Okay!”

PownceAIM
cue to PownceAIM that
request token has been
user tells
PownceAIM authorized
that auth is
complete

PownceAIM Pownce
API calls
ask for access Authorization: OAuth realm=\"http://api.pownce.com/\",
token with oauth_consumer_key=\"nbe958225r999a706d1u4qgwx2nx9e8j\",
authorized oauth_token=\"3fjay66o4x78j4c8\",
oauth_signature_method=\"HMAC-SHA1\",
request token oauth_signature=\"6A87eXJ8MimMnCHfRM1hedEPHG4%3D\",
oauth_timestamp=\"1211258114\",
oauth_nonce=\"F85482A6-B1BC-4580-95B2-0E51300CBEF7\",
oauth_version=\"1.0\"
request token
PownceAIM stores exchanged for
access token access token
oauth_token_secret=3w6z92eb1s86a48t&oauth_token=oixvd0538vmw3hm2

PownceAIM Pownce
API calls
ask for Authorization: OAuth realm=\"http://api.pownce.com/\",
protected resource oauth_consumer_key=\"nbe958225r999a706d1u4qgwx2nx9e8j\",
oauth_token=\"oixvd0538vmw3hm2\",
(note list) oauth_signature_method=\"HMAC-SHA1\",
oauth_signature=\"YXQ%2Fq3B1ZR4XOQf8bwSMh+tcSL8%3D\",
oauth_timestamp=\"1211258746\",
oauth_nonce=\"DE648679-003B-42B5-806A-F185D0714EEB\",
oauth_version=\"1.0\"
<?xml version=\"1.0\" encoding=\"utf-8\"?>
return API
<notes>
<note>
data
<body>Check out my website Leah!</body>
<permalink>http://pownce.com/iamcal/notes/2211344/</permalink>
<sender>
<user>
<username>iamcal</username>
...

Managing Tokens
• request token expiration
• access token expiration
• end user token management

Token Management
http://pownce.com/settings/applications

HTTP Errors
• 400 Bad Request
• unsupported parameter
• unsupported signature method
• missing required parameter
• duplicate OAuth parameter
• 401 Unauthorized
• invalid consumer key
• invalid / expired token
• invalid signature (signature does not match)
• invalid / used nonce

Common Errors
• signature does not match
• providers can show expected base string
• token is invalid
• expired? wrong type of token?
• request token unauthorized
• user needs to login to authorize the
request token

Testing Tools
• web-based test server and client by Andy
Smith (http://term.ie/oauth/example)
• Endpointr, mac desktop app by Jon Crosby

Issues
• service provider documentation
• files
• granular permissions
• timestamp and nonce verification
• vague tokentokens consumers check
expiration,
for expired

Current Status
• OAuth Core 1.0 Final (Dec 2007)
• OAuth Discovery 1.0 Draft 2
• Libraries: • coldfusion
• csharp
• java
• javascript
• maven
• obj-c
• obj-c1
• perl
• php
• python
• ruby

Service Provider
Implementations
• 88 Miles
• Google Contacts API
• Ma.gnolia
• Pownce
• Thmbnl
• Yahoo! Fire Eagle
http://wiki.oauth.net/ServiceProviders

More Info
• main site: http://oauth.net
• spec: http://oauth.net/core/1.0
• code: http://code.google.com/p/oauth
• mailing list: http://groups.google.com/group/oauth
• wiki: http://wiki.oauth.net
• Pownce API: http://pownce.com/api

Thanks!
ugly logo!