OAuth 2.0 Quick Guide

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OAuth 2.0 - Quick Guide
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OAuth 2.0 - Overview
What is OAuth 2.0?
OAuth is an open authorization protocol, which allows accessing the resources of the
resource owner by enabling the client applications on HTTP services such as Facebook,
GitHub, etc. It allows sharing of resources stored on one site to another site without using
their credentials. It uses username and password tokens instead.
OAuth 2.0 is developed by the IETF OAuth Working Group, published in October 2012.

Why Use OAuth 2.0?
You can use OAuth 2.0 to read data of a user from another application.
It supplies the authorization workflow for web, desktop applications, and mobile
devices.
It is a server side web app that uses authorization code and does not interact with
user credentials.

Features of OAuth 2.0
OAuth 2.0 is a simple protocol that allows to access resources of the user without
sharing passwords.
It provides user agent flows for running clients application using a scripting
language, such as JavaScript. Typically, a browser is a user agent.
It accesses the data using tokens instead of using their credentials and stores data
in online file system of the user such as Google Docs or Dropbox account.

Advantages of OAuth 2.0
OAuth 2.0 is a very flexible protocol that relies on SSL (Secure Sockets Layer that
ensures data between the web server and browsers remain private) to save user
access token.
OAuth 2.0 relies on SSL which is used to ensure cryptography industry protocols
and are being used to keep the data safe.
It allows limited access to the user's data and allows accessing when authorization
tokens expire.
It has ability to share data for users without having to release personal
information.
It is easier to implement and provides stronger authentication.

Disadvantages of OAuth 2.0
If you are adding more extension at the ends in the specification, it will produce a
wide range of non-interoperable implementations, which means you have to write
separate pieces of code for Facebook, Google, etc.
If your favorite sites are connected to the central hub and the central account is
hacked, then it will lead to serious effects across several sites instead of just one.

OAuth 2.0 - Architecture
In this chapter, we will discuss the architectural style of OAuth 2.0.

Step 1 − First, the user accesses resources using the client application such as Google,
Facebook, Twitter, etc.
Step 2 − Next, the client application will be provided with the client id and client password
during registering the redirect URI (Uniform Resource Identifier).
Step 3 − The user logs in using the authenticating application. The client ID and client
password is unique to the client application on the authorization server.
Step 4 − The authenticating server redirects the user to a redirect Uniform Resource
Identifier (URI) using authorization code.
Step 5 − The user accesses the page located at redirect URI in the client application.
Step 6 − The client application will be provided with the authentication code, client id and
client password, and send them to the authorization server.
Step 7 − The authenticating application returns an access token to the client application.
Step 8 − Once the client application gets an access token, the user starts accessing the
resources of the resource owner using the client application.
OAuth 2.0 has various concepts, which are briefly explained in the following table.
Sr.No.

Concept & Description

Terminology

OAuth provides some additional terms to understand the concepts of
authorization.
Web Server
2

Web server delivers the web pages and uses HTTP to serve the files that forms
the web pages to the users.
User-Agent

The user agent application is used by client applications in the user's device,
which acts as the scripting language instance.
Native Application

Native application can be used as an instance of desktop or mobile phone
application, which uses the resource owner password credentials.

OAuth 2.0 - Client Credentials
The client credentials can be used as an authorization grant when the client is the resource
owner, or when the authorization scope is limited to protected resources under the control
of the client.
The client requests an access token only with the help of client credentials.
The client credentials authorization flow is used to acquire access token to
authorize API requests.
Using client credentials authorization, access token which is acquired, only grants
permission for your client application to search and get catalog documents.
The following figure depicts the Client Credentials Flow.

The flow illustrated in the above figure consists of the following steps −
Step 1 − The client authenticates with the authorization server and makes a request for
access token from the token endpoint.

Step 2 − The authorization server authenticates the client and provides access token if it's
valid and authorized.
The following table lists the concepts of Client Credentials.
Sr.No.

Concept & Description
Obtaining End-User Authorization

The authorization end point is typically URI on the authorization server in which
the resource owner logs in and permits to access the data to the client
application.
Authorization Response

The authorization response can be used to get the access token for accessing
the owner resources in the system using the authorization code.
Error Response and Codes

The authorization server responds with a HTTP 400 or 401 (bad request) status
codes, if an error occurs during authorization.

OAuth 2.0 - Obtaining an Access Token
An access token is a string that identifies a user, an application, or a page. The token
includes information such as when the token will expire and which app created that token.
First, it is necessary to acquire OAuth 2.0 client credentials from API console.
Then, the access token is requested from the authorization server by the client.
It gets an access token from the response and sends the token to the API that you
wish to access.
You must send the user to the authorization endpoint at the beginning. Following is an
example of a dummy request
https://publicapi.example.com/oauth2/authorize?client_id=your_client_id&redirect_uri=your_url
&response_type=code

Following are the parameters and their descriptions.
client_id − It should be set to the client id of your application.
redirect_uri − It should be set to the URL. After the request is authorized, the
user will be redirected back.
response_type − It can either be a code or a token. The code must be used for
server side applications, whereas the token must be used for client side

applications. In server side applications, you can make sure that the secrets are
saved safely.
Following table lists the concepts of Client Credentials.
Sr.No.

Concept & Description
Authorization Code

The authorization code allows accessing the authorization request and grants

access to the client application to fetch the owner resources.
Resource Owner Password Credentials

The resource owner password credentials include only one request and one

response, and is useful where the resource owner has a good relationship with
the client.
Assertion

Assertion is a package of information that makes the sharing of identity and

security information across various security domains possible.
Refresh Token

The refresh tokens are used to acquire a new access tokens, which carries the

information necessary to get a new access token.
Access Token Response

Access token is a type of token that is assigned by the authorization server.
Access Token Error Response Codes

If the token access request, which is issued by the authorization server is

invalid or unauthorized, then the authorization server returns an error
response.

OAuth 2.0 - Accessing a Protected Resource
The client provides an access token to the resource server to access protected resources.
The resource server must validate and verify that the access token is valid and has not
expired.
There are two standard ways of sending credentials −
Bearer Token − The access token can only be placed in POST request body or
GET URL parameter as a fallback option in the authorization HTTP header.

They are included in the authorization header as follows −
Authorization: Bearer [token-value]

For Example −
GET/resource/1 HTTP /1.1
Host: example.com
Authorization: Bearer abc...

MAC − A cryptographic Message Authentication Code (MAC) is computed using
the elements of the request and is sent to the authorization header. Upon receiving
the request, the MAC is then compared and computed by the resource owner.
The following table shows the concepts of accessing protected resource.
Sr.No.

Concept & Description
Authenticated Requests

It is used to get the authorization code token for accessing the owner resources
in the system.
The WWW-Authenticate Response Header Field

The resource server includes the "WWW-Authenticate" response header field, if
the protected resource request contains an invalid access token.

OAuth 2.0 - Extensibility
There are two ways in which the access token types can be defined −
By registering in the access token type's registry.
By using a unique absolute URI (Uniform Resource Identifier) as its name.

Defining New Endpoint Parameters
Parameter names must obey the param-name ABNF (Augmented Backus-Naur Form is a
metalanguage based on Backus-Naur Form consisting of its own syntax and derivation
rules) and the syntax of parameter values must be well-defined.
param-name = 1* name-char
name-char = "-" / "." / "_" / DIGIT / ALPHA

Defining New Authorization Grant Types

New authorization grant types can be assigned a distinct absolute URI for use, with the
help of "grant_type" parameter. The extension grant type must be registered in the OAuth
parameters registry, if it requires additional token endpoint parameters.

Defining New Authorization Endpoint Response Types
response-type = response-name *(SP response-name)
response-name = 1* response-char
response-char = "_" / DIGIT / ALPHA

The response type is compared as space-delimited list of values, if it has one or more
space characters where the order of the values does not matter and only one order of
value can be registered.

Defining Additional Error Codes
The extension error codes must be registered, if the extensions they use are either a
registered access token, or a registered endpoint parameter. The error code must obey the
error ABNF (Augmented Backus-Naur Form) and when possible it should be prefixed by a
name identifying it.
error = 1 * error_char
error-char =

%x20-21 / %x23-5B / 5D-7E

OAuth 2.0 - IANA Considerations
IANA stands for Internet Assigned Numbers Authority which provides the information
about the registration values related to the Remote Authentication Dial In User Service
(RADIUS).
IANA includes the following considerations −

OAuth Access Token Types Registry
OAuth access tokens are registered by experts with required specification. If they are
satisfied with the registration, only then they will publish the specification. The registration
request will be sent to the @ietf.org for reviewing with the subject ("Request for access
token type: example"). Experts will either reject or accept the request within 14 days of
the request.

Registration Template
The registration template contains the following specifications −
Type Name − It is the name of the request.

Token Endpoint Response Parameters − The additional access token response
parameter will be registered separately in OAuth parameters registry.
HTTP Authentication Scheme − The HTTP authentication scheme can be used to
authenticate the resources by using the access token.
Change Controller − Give the state name as "IETF" for standard track RFCs, and
for others, use the name of the responsible party.
Specification Document − The specification document contains the parameter
that can be used to retrieve a copy of the document.

OAuth Parameters Registry
OAuth parameters registry contains registration of authorization endpoint request or
response, token endpoint request or response by the experts with the required
specification. The registration request will be sent to the experts and if they are satisfied
with registration, then they will publish the specification.

Registration Template
The registration template contains specifications such as Type Name, Change Controller
and Specification Document as defined in the above OAuth Access Token Types Registry
section, except the following specification −
Parameter Usage Location − It specifies the location of the parameter such as
authorization request or response, token request or response.

Initial Registry Contents
The following table shows OAuth parameters registry containing the initial contents −
Sr.No.

Parameter Name & Usage Location

Change
Controller

Specification
Document

client_id
1

authorization request, token request

IETF

RFC 6749

IETF

RFC 6749

IETF

RFC 6749

IETF

RFC 6749

client_secret
2

token request
response_type

authorization_request
redirect_uri

authorization request, authorization
scope
5

authorization request or response, token

IETF

RFC 6749

IETF

RFC 6749

IETF

RFC 6749

IETF

RFC 6749

IETF

RFC 6749

IETF

RFC 6749

IETF

RFC 6749

IETF

RFC 6749

IETF

RFC 6749

IETF

RFC 6749

IETF

RFC 6749

request or response
state
6

authorization request or response
code

token request, authorization response
error_description

authorization response, token response
error_uri

authorization response, token response
grant_type

token request
access_token

authorization response, token response
token_type

authorization response, token response
expires_in

authorization response, token response
username

token request
password

token request

IETF

refresh_token

RFC 6749

token request, token response

OAuth Authorization Endpoint Response Type Registry
This can be used to define OAuth Authorization Endpoint Response Type Registry. The
response types are registered by experts with the required specification and if they are
satisfied with the registration, only then they will publish the specification. The registration

request will be sent to the @ietf.org for reviewing. The experts will either reject or accept
the request within 14 days of the request.

Initial Registry Contents
The following table shows the authorization endpoint response type registry containing the
initial contents.
Sr.No.

Parameter Name

Change Controller

Specification Document

code

IETF

RFC 6749

token

IETF

RFC 6749

OAuth Extensions Error Registry
This can be used to define OAuth Extensions Error Registry. The error codes along with
protocol extensions such as grant types, token types, etc. are registered by experts with
the required specification. If they are satisfied with the registration, then they will publish
the specification. The registration request will be sent to the @ietf.org for reviewing with
subject ("Request for error code: example"). Experts will either reject or accept the
request within 14 days of the request.

Registration Template
The

registration

template

contains

specifications

such

Change

Controller

and

Specification Document as defined in the above OAuth Access Token Types Registry
section, except the following specifications −
Error Name − It is the name of the request.

Error Usage Location − It specifies the location of the error such as authorization
code grant error response, implicit grant response or token error response, etc,
which specifies where the error can be used.
Related Protocol Extension − You can use protocol extensions such as extension
grant type, access token type, extension parameter, etc.

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