Open Authentication Introduction Definitions Protocol Workflow OAuth Tokens Security Architecture OAuth and Twitter Coding Oauth Demo Troubleshooting
OAuth? Oaths is an authorization standard for API’s that does away with logins and passwords to grant authorization to a third-party
Why OAuth? Every day a new websites are launched which tie services from different sites and offer you
OAuth Definitions Service provider The website or web-service where the restricted resources are located User User have ‘stuff’ they don’t want to make pubic on the service provider but they do want to share it with another site Consumer The name for the application trying access the users resources Protected Resources The ‘stuff’ oauth protects and allow access. Tokens Tokens are used instead of user credentials to access resources
OAuth : Protocol Workflow
Jane wants to share some of her vacation photos with her friends. Jane uses Faji, a photo sharing site, for sharing journey photos. She signs into her faji.com account, and uploads two photos which she marks private. Using OAuth terminology Jane is the User Faji is the Service Provider. The 2 photos Jane uploaded are the Protected Resources. OAuth Example
Jane wants to share them with her grandmother. But grandma doesn’t have an internet connection so Jane plans to order prints and have them mailed to grandma. Being a responsible person, Jane uses Beppa, an environmentally friendly photo printing service. Using OAuth terminology, Beppa is the Consumer. Beppa must use OAuth to gain access to the photos in order to print them.
When Beppa added support for Faji photo import, a Beppa developer known in OAuth as a Consumer Developer obtained a Consumer Key and Consumer Secret from Faji to be used with Faji’s OAuth-enabled API. Using OAuth terminology, Consumer Key Consumer secret
Beppa requests from Faji a Request Token. At this point, the Request Token is not User-specific, and can be used by Beppa to gain User approval from Jane to access her private photos. Using OAuth terminology, Request Token
When Beppa receives the Request Token, it redirects Jane to the Faji OAuth User Authorization URL with the Request Token and asks Faji to redirect Jane back once approval has been granted to http://beppa.com/order. Using OAuth terminology, Oauth User Authorization URL Call Back URL
After successfully logging into Faji, Jane is asked to grant access to Beppa, the Consumer. Faji informs Jane of who is requesting access (in this case Beppa) and the type of access being granted. Jane can approve or deny access.
Jane waits for Beppa to present her with her photos fetched from her Faji account.
While Jane waits, Beppa uses the authorized Request Token and exchanges it for an Access Token. Request Tokens are only good for obtaining User approval, while Access Tokens are used to access Protected Resources, in this case Jane’s photos. In the first request, Beppa exchanges the Request Token for an Access Token and in the second (can be multiple requests, one for a list of photos, and a few more to get each photo) request gets the photos. Using OAuth terminology, Access Token
Jane is very impressed how Beppa grabbed her photos without asking for her username and password. She likes what she sees and place the print order.
Tokens OAuth uses three types of credentials Client credentials (consumer key and secret) Temporary credentials (request token and secret) Token credentials (access token and secret)
Client Credentials Allows server to authenticate server Allows server to get information about the client Oauth_consumer_key Oauth_consumer_secret
Token Credentials Token credentials are in place of username and password The client uses token credentials to access resource owner protected resource Token credentials are limited in scope and duration Oauth_access_token Oauth_access_secret
Temporary credentials Used to identify the authorization request To accommodate different clients like desktop, mobile etc. Add extra flexibility and security Oauth_token Oauth_token_secret
OAuth Security Architecture
Signature and Hash OAuth uses digital signatures instead of sending the full credentials (specifically, passwords) with each request. The sender uses a mathematical algorithm to calculate the signature of the request and includes it with the request.
Hash Algorithm A common way to sign digital content is using a hash algorithm. Hashing is the process of taking data (of any size) and condensing it to a much smaller value (digest) in a fully reproducible (one-way) manner This means that using the same hash algorithm on the same data will always produce the same smaller value Hashing usually does not allow going from the smaller value back to the original.
Shared Secret By itself, hashing does not verify the identity of the sender, only data integrity. In order to allow the recipient to verify that the request came from the claimed sender, the hash algorithm is combined with a shared secret If both sides agree on some shared secret known only to them, they can add it to the content being hashed.
Nonce(‘Number used Once’) What is missing is something to prevent requests intercepted by an unauthorized party, usually by sniffing the network, from being reused. This is known as a replay attack. Able to make the same sign request over and over again. To prevent compromised requests from being used again (replayed), OAuth uses a nonce and timestamp. By having a unique identifier for each request, the Service Provider is able to prevent requests from being used more than once
TimeStamp Using nonces can be very costly for Service Providers as they demand persistent storage of all nonce values received, ever. OAuth adds a timestamp value to each request which allows the Service Provider to only keep nonce values for a limited time. When a request comes in with a timestamp that is older than the retained time frame, it is rejected as the Service Provider no longer has nonces from that time period.
Signature Methods OAuth defines 3 signature methods used to sign and verify requests PLAINTEXT HMAC-SHA1 RSA-SHA1 When signing requests, it is necessary to specify which signature method has been used to allow the recipient to reproduce the signature for verification The decision of which signature method to use depends on the security requirements of each application
Signature Base String Not only must they both use the same algorithm and share secret, but they must sign the same content. This requires a consistent method for converting HTTP requests into a single string which is used as the signed content — the Signature Base String..
Getting the Request Token Building a reqestToken request requires the following: HTTP Method, Request URI, oauth_callback, oauth_consumer_key, oauth_nonce, oauth_signature_method, oauth_timestamp oauth_version
Getting the Request Token
First build your string to sign
Getting the Request Token First build your string to sign These parameters get sorted alphabetically, each value is URL escaped, and than concatenated into a single string.
Create your Authorization HTTP Header & and Issue the request Now we sign this string using our consumer secret and create an HTTP Authorization header. The signature should be placed in the oauth_signature value Getting the Request token
Now we issue this request to the requestToken endpoint, and if all is sucessful,you will get something like the following URL encoded response: The oauth_token field is now your request token, and the oauth_token_secret will be used for signing your request for an access toen.oaut_callback_confirmed just gives you confirmation the we recognized your oauth_callback parameter You will want to “hold on” to oauth_token and oauth_token_secret until you have completed the access token step Evaluate the Request Token
Now that we have a request token, we can build the url to authorize the user. we will then redirect the user to this url so they can grant your application access. An authorization url is simply this end point: https://api.twitter.com/oauth/authorize with a query parameter tacked on called oauth_token.the value for this parameter is equal to the request token you received in the previous step. The user needs to land on this page within 5 minutes of your request take cycle. you should not pass an oauth_callback parameter to this page(you already did that in the request token step) Authorizing the member Build your Authorization URL https://api.twitter.com/oauth/authorize?oauth_token=O6npS44e8ZPQfVcYfHVTGXtnLVBQ4xn8Wu2eBFtPNQ
Send the user to Twitter Authorization Page The user will then be sent to our authorization page. when completed the user will either be sent back to your oauth_callback URL or presented with a series of digits they will be instructed to hand-enter into your application(if you are performing out-of-band authentication) Authorizing the member
Prepare your singing secret Regardless of whether you used out-of-band authentication or not, you will now be equipped with a request token an oauth_token_secret and an oauth_verfier.you are now going to exchange that request token for an access token, imbued with permission of the Twitter member to act on their behalf Getting an Access token
Getting the Access Token
First build your string to sign
First build your string to sign These parameters get sorted alphabetically, each value is URL escaped, and than concatenated into a single string. Getting the Access Token
Create your Authorization HTTP Header & and Issue the request Now we sign this string using our request token secret and create an HTTP Authorization header. The signature should be placed in the oauth_signature value Getting the Access token
Now we issue this request to the aceessToken endpoint, and if all is sucessful,you will get something like the following URL encoded response: The oauth_token field is now your access token, and the auth_toke_secert will be used for signing all request on behalf of the member. You will want to “hold on” to oauth_token and oauth_token_secret until you have completed the access token step Evaluate the Access Token
Oauth is complicated, and there are a number of things that go wrong. Here are some tips. Every error response we send you will contain an xml body describing the error, including a timestamp representing server time. Some oauth-based requests will also return an OAUTH_PROBLEM http header Make sure that your server’s system clock is in sync with ours Oauth_callback should only be provided on the request token step. Oauth_verifier is required in the access Token. PUT & POST operations typically have xml content-types. your oauth library should exclude the request body in signature calculations as a result. For the access token step, remember that the request tokens oauth_token_secret must be used as part of your signing key Likewise, for all resource requests, your access tokens oauth_token_secret must be used as part of your signing key. Troubleshooting