OAuth?

Oaths is an authorization standard for API’s that does away with logins and passwords to grant authorization to a third-party

Every day a new websites are launched which tie services from different sites and offer you

Why OAuth?

Service providerThe website or web-service where the restricted resources are located

UserUser 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 ResourcesThe ‘stuff’ oauth protects and allow access.

TokensTokens are used instead of user credentials to access resources

OAuth Definitions

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.

OAuth uses three types of credentials

◦ Client credentials (consumer key and secret)◦ Temporary credentials (request token and

secret)◦ Token credentials (access token and secret)

Tokens

◦ Allows server to authenticate server◦ Allows server to get information about the client

Oauth_consumer_key Oauth_consumer_secret

Client 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

Token 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

Temporary credentials

OAuth Security Architecture

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.

Signature and Hash

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.

Hash Algorithm

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.

Shared Secret

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

Nonce(‘Number used Once’)

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.

TimeStamp

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 Methods

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.. 

Signature Base String