OAuth 2+ API Security

API and Managing API

• Private APIs , Public APIs(twitter, facebook)

• Even though these APIs are public there must be a access control (e.g.: any one else can’t update your FB status on behalf of you)

Securing APIs(before OAuth)

•Basic auth – Sending user credentials in http authentication header

•Mutual Authentication - based on certificates, server authenticate to client , client to server

Problem ..?ONLY 2 Parties

What Happens if a 3rd party (client/app) wants to call APIs on

behalf of you

Need A Better method

Why we need a better method

• Third party applications can not save password as a salted hash but in clear text as they will use user credentials later to access resources.

• Resource owner can not limit the time of access or what resources to access by clients to his resources.

• Resource owners cannot revoke access to an individual third party. To revoke access resource owner has to change password which will automatically revoke all other clients.

• Compromise of any third‐party application results in compromise of the end-user's password and all of the data protected by that password.

Why we need a better method

Pre OAuth Era•Google oauth

•Flicker oauth

•Yahoo BB-oauth

OAuth 2.0

4 Roles

Resource Owner

Resource ServerClient

Authorization Server

Resource Owner

• An entity capable of granting access to a protected resource

• When the resource owner is a person, it is referred to as an end‐user.

Resource Server

The server hosting the protected resources, capable of accepting and responding to protected resource requests using access tokens.

Client

An application making protected resource requests on behalf of the resource owner and with its authorization

2 types,

• Confidential clients- can securely keep client_secret and client_id(eg:Web application)• Public clients(eg: Browser based clients, mobile apps)

Authorization Server

The server issuing access tokens to the client after successfully authenticating the resource owner and obtaining authorization

OAuth 2 (A) Authorization Request

(B) Authorization Grant

(C) Authorization Grant

(D) Access Token

(E) Access Token

(F) Protected Resource

Resource owner

Authorization Server

Resource Server

Client

OAuth 2 (A) Give me the key of your car

(B) It’s with key holder, I will give you a chit, show this to key holder and ask for key. You can’t open my private stuff box with this key

(C) Give me car key. Here is the chit of approve from owner

(D) Ok, This is accepted, here is the key

(E) Give me car to repair, this is the key

(F) Ok, have the car

Car owner

Key Holder

Car park

Mechanic

OAuth 2 (A) Authorization Request

(B) Authorization Grant

(C) Authorization Grant

(D) Access Token

(E) Access Token

(F) Protected Resource

Resource owner

Authorization Server

Resource Server

Client

Implicit

Resource Owner Password Credentials

Client Credentials

Authorization Code

Authorization Code

User Agent

Client

Resource owner

Authorization Server

(A) Client Identifier & redirect URL

(B) User Authenticates(C) Authorization Code

(B)

(A) (C)

(D) Authorization Code & Redirect URI

(E) Access Token

Scope

Scope• Scope indicates what resource client wants access and which actions he wants to perform on that.

• The value of the scope parameter is expressed as a list of space-delimited, case sensitive strings which are defined by authorization server.

• The authorization server MAY fully or partially ignore the scope requested by the client, based on the authorization server policy or the resource owner's instructions.

Authorization Code

User Agent

Client

Resource owner

Authorization Server

(A) Client Identifier & redirect URL

(B) User Authenticates(C) Authorization Code

(B)

(A) (C)

(D) Authorization Code & Redirect URI

(E) Access Token

Confidential Client Type

Web application

Authorization Code

User Agent

Client

Resource owner

Authorization Server

(A) Client Identifier & redirect URL

(B) User Authenticates(C) Authorization Code

(B)

(A) (C)

(D) Authorization Code & Redirect URI

(E) Access Token

Scope

Client Authenticates to authorization server

Basic Auth Client_ID/Client_secret

Authorization Code - Benefits

• Because the resource owner only authenticates with the authorization server, the resource owner's credentials are never shared with the client.

• Access token is given directly to the client without passing it through the resource owner's user-agent

Authorization Grant Request

•response_type:REQUIRED.Value MUST be set to "code".

• client_id: REQUIRED. The client identifier.

• redirect_url: OPTIONAL. Where to be redirected by the Authorization Server

• scope: OPTIONAL. The scope of the access request.

• state : RCOMMENDED. An opaque value used by the client to maintain state between the request and callback.

Authorization Code

Authorization Grant Request

https://oauth2server.com/auth?response_type=code& client_id=CLIENT_ID&redirect_uri=REDIRECT_URI&scope=photos

Authorization Code

Authorization Grant Response

• code :REQUIRED. The authorization code generated by the authorization server

• state : REQUIRED .if the "state" parameter was present in the client authorization request.

Authorization Code

https://oauth2client.com/cb?code=AUTH_CODE_HERE

Access Token Request

• grant_type :REQUIRED. Value MUST be set to "authorization_code"

• code : REQUIRED . The authorization code received from the Authorization Server.

• redirect_uri: REQUIRED,if the "redirect_uri" parameter was inclued in the authoization

POST https://api.oauth2server.com/token grant_type=authorization_code& code=AUTH_CODE_HERE& redirect_uri=REDIRET_URI&client_id=CLIENT_ID& client_secret=CLIENT_SECRET

Authorization Code

Access Token Response

•access_token : REQUIRED.The access token issued by the authorization server.

•token_type : REQUIRED.The type of the token. Value is case insensitive.

•expires_in : RECOMMENDED.The lifetime in seconds of the access token

Authorization Code

Access Token

• Credentials used to access protected resources• A string representing an authorization issued to the client.• Tokens represent specific scopes and durations of accessRefresh Token

• Used to obtain a new access token when the current access token becomes invalid or expires.• Can use to obtain additional access tokens with identical or narrower scope

Access Token Response

{ "access_token":"RsT5OjbzRn430zqMLgV3Ia"}

Authorization Code

The implicit grant is a simplified authorization code flow optimized for clients implemented in a browse using a scripting language such as JavaScript

Implicit

User Agent

Client

Resource owner

Authorization Server

(A) Client Identifier & redirect URL

(B) User Authenticates

(C) Redirection URI with access token in fragment

(B)

(A) (C)

(D) Redirection URI without fragment

(E) Script

Scope

Implicit

Web hosted client resource

•The authorization server does not authenticate the client.

• Improve the responsiveness and efficiency of some clients (such as a client implemented as an in-browser application), since it reduces the number of round trips required to obtain an access token.

Implicit

User Agent

Client

Resource owner

Authorization Server

(A) Client Identifier & redirect URL

(B) User Authenticates

(C) Redirection URI with access token in fragment

(B)

(A) (C)

(D) Redirection URI without fragment

(E) Script

Scope

Implicit

Web hosted client resource

Public client Type

User Agent based Application

Authorization Grant Request

• response_type: REQUIRED.Value MUST be set to ”token".• client_id : REQUIRED. The client identifier.• redirect_uri : OPTIONAL. Where to be redirected by the Authorization Server.• scope : OPTIONAL. The scope of the access request.• state : RECOMMENDED.An opaque value used by the client to maintain state between the request and callback.

https://oauth2server.com/auth?response_type=token&client_id=CLIENT_ID&redirect_uri=REDIRECT_URI&scope=photos

Implicit

Access Token Response• access_token : REQUIRED.The access token issued by the authorization server.• token_type : REQUIRED. The type of the token. Value is case insensitiv.• expires_in : RECOMMENDED. The lifetime in seconds of the access token• scope : OPTIONAL, if identical to the scope requested by the client, otherwise REQUIRED.• state : REQUIRED if the "state" parameter was present in the client authorization request

https://oauth2client.com/cb#token=ACCESS_TOKEN

Implicit

Client credentials are used as an authorization grant

when the client is also the resource owner. or

is requesting access to protected resources based on an authorization previously arranged with the

authorization server.

Client Credentials

Client Credentials

Authorization ServerClient

(A) Client Authentication

(B) Access Token

Client Credentials

Authorization ServerClient

(A) Client Authentication

(B) Access Token

Confidential Client Type

Access Token request

• grant_type : REQUIRED. Value MUST be set to ”client_credentials".

• scope: OPTIONAL. The scope of the access request.

POST https://api.oauth2server.com/token grant_type=client_credentials client_id=CLIENT_ID&client_secret=CLIENT_SECRET

•access_token : REQUIRED. The access token issued by the authorization server.

•token_type : REQUIRED. The type of the token. Value is case insensitive.

•expires_in : RECOMMENDED. The lifetime in seconds of the access token

Access Token Response

Resource owner password credentials

Resource owner

Authorization Server

(A) Resource owner password credentials

(B) Resource owner password credentials

(C) Access token

Client

When to use•In mobile applications

▫Will exchange your user name password to a access token and only store this access token in mobile app.

▫It should only be used by apps created by the service itself.(eg: the native Twitter app)

Token Request

POST https://api.oauth2server.com/token granttype=password username=USERNAME& password=PASSWOD&client_id=CLIENT_ID

Resource owner password credentials

References•OAuth 2.0 Authorization Framework, specification

•OAuth 2 implified , Aron Parecki

•Oauth 2.0 with pet care house , Prabath Siriwardena