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What is OAuth? A Beginner's Guide to Authentication for APIs

Secure your digital world with OAuth authentication. Learn how OAuth enhances online safety and simplifies user access. Explore our comprehensive guide now.

Written by RamotionOct 5, 202312 min read

Last updated: Oct 5, 2023

Defining OAuth

sharing data between applications and services is essential. However, sharing sensitive user data also introduces security risks if not done correctly. OAuth is an open standard that enables secure data sharing and access delegation between applications. It allows users to grant limited access to their accounts and data to third-party applications without compromising their passwords.

OAuth is an authorization framework that provides client applications with secure delegated access to user accounts on an HTTP service through tokens. OAuth 2.0 is currently the most widely accepted and widely used version of OAuth, and it has been adopted by major web services like Facebook, X (Twitter), Google, Microsoft, LinkedIn, and more.

The OAuth authentication protocol was developed by the Internet Engineering Task Force (IETF) in 2006 as an open standard for authorization. It was created to solve the problem of building applications that require user authorization but want to rely on something other than passwords.

The initial version of the protocol was published in January 2007, while the final version was published in June 2007 and has been ratified as an IETF standard since then. The OAuth 2.0 specification was released in 2012 and contains many improvements over its predecessor.

OAuth 2.0 is an authorization framework that allows a third-party application to obtain limited access to an HTTP service on behalf of a resource owner. The authorization protocol improves upon the original OAuth by supporting resource owners and providing more granular access control.

In addition, it defines the use of both client credentials and security tokens and how they should be exchanged between parties.

When using a website or mobile app, you often must enter your username and password. This gives the app permission to access your account. But it also means that anyone who gets their hands on your login details can access all your data.

OAuth is designed to solve this problem by giving you much more control over how programs interact with your accounts.

The problem OAuth aims to solve is how to let users grant third-party access to their accounts without sharing their password with the application or website. The solution proposed by OAuth is to utilize an access token, which can be revoked if compromised, instead of a password that must be updated every time it is used.

Why use OAuth?

OAuth is an open standard that defines the roles, endpoints, and messages used to implement authorization flows between clients (like your app) and servers (like an API). It allows users to share information with other applications without sharing their username or password; instead, these apps obtain temporary access tokens generated by our server after requesting authorization from the user via a browser redirect flow.

These tokens can then be used to call the API on behalf of that user for a certain period until they expire or the user revokes the app’s access.

The main reason for this is that it provides a secure way to allow third-party applications access to user data without giving them the user's password. This makes it much easier than other authentication methods, such as Basic Auth or API keys, because you don't have to manage passwords or keys.

It also gives you more control over permissions and allows different authorization methods, such as refresh tokens, which can be used to refresh access tokens when they expire.

OAuth is most commonly used with mobile apps or web pages that want access to your Google account data (such as Calendar events). However, it can be used almost anywhere you need access to end user information on an external site or service (for example, Facebook, Twitter, LinkedIn).

OAuth and APIs

OAuth is an open standard for authorization. This means that it can be used by any application or service to allow access to protected resources. The Internet Engineering Task Force (IETF) maintains the OAuth standard and is currently on version 2 of its specification.

APIs are a type of interface that enables two or more applications to interact with each other. APIs help businesses connect to their customers and partners, which allows them to build more efficient applications and services.

APIs are also used to connect applications. For example, an API can be used to provide access to data stored in a database. This means that you don’t have to write your database code but instead use the API provided by the database company.

Similarly, OAuth can be used between two applications (a web application and a mobile application) or between businesses and their customers (for example, Facebook Connect).

How OAuth is used to secure APIs

OAuth provides a mechanism for granting third-party applications access to protected resources on behalf of the resource owner, who must always be present during authorization. The resource owner can grant access using one or more credentials (e.g., username/password combination) from the API provider’s website, mobile app, or desktop application.

OAuth is typically used to secure APIs that allow web app developers to access data and services. Developers can use OAuth to create applications that interact with the API provider’s service as a user would, without exposing confidential user credentials or other sensitive information. For example, if an API allows users to post status updates on their profiles, an application could use OAuth to ask for permission to post a specific message on behalf of a resource owner.

The role of OAuth in the API economy

API economy refers to the ecosystem where companies create products and services that leverage APIs for integration. These products include:

  • Mobile apps - A mobile app is an application that runs on a smartphone device such as an iPhone or Android phone; it interacts with an API provider’s software platform via an API. Mobile apps can also be used to create new services, such as an app that lets people order food from restaurants or another app that helps users manage their finances.
  • Web applications - A web application is software that runs on a server and provides functionality via an API. Users can access it through their browser, but it isn’t limited to one device like a mobile app.

OAuth Central Components

The main components of the OAuth protocol are:

Resource owner

The resource owner is the user or client with control to access resources. They are represented by a combination of their username and password.

The resource owner also has the option to delegate their authorization rights to another user. This is called a “delegation token” and allows the client application to request access tokens on behalf of another user.


A client is an application that wants to access a user's resources from another application. This can be done with or without their consent.

The client application must be registered with the resource owner’s authorization server. This is usually done through an application registration process where the client registers their app and receives credentials that can be used to request authorization tokens.

Resource Server

The resource server is the application that holds the user’s data and is responsible for responding to client requests. When clients want to access a user's resources, they send an authorization request to the resource server.

This request includes information about what access they would like (for example, read-only or write) and who makes the request (the client ID). The resource server then decides whether or not to approve this request based on the rules defined by its authorization policy.

Authorization server

The authorization server issues access tokens and manages the relationship between clients and resource owners (those who have control over their data). It also verifies the authenticity of both parties before they exchange information with each other.

The resource server then checks the access token to see if it’s valid before granting access to resources. The authorization server does not store any user data or passwords but instead stores information about each client's permissions and how long that access should last.

This means that even if someone gains unauthorized access to an account on your app (for example, through a password breach), they won’t be able to get any information from your users’ accounts without the correct authorization code.

Access Token

An access token is a string of characters representing the authorization granted to a client by an authorization server. It contains information about the user, like their name and email address, as well as what permissions they have granted for the app to use on their behalf.

When you log in with your username and password, your account will be authenticated, and the authorization server will issue an access token back to you.


A scope is a list of actions that the user has granted your app permission to perform on their behalf. This can include accessing their email address, reading their contacts, or posting on their social media accounts. You should always check what scopes an API requires before you start using it in your application code.

How Does OAuth Work

OAuth is an authentication protocol that allows two applications to communicate and share data without exposing the user’s password. It uses a combination of security tokens and HTTP redirects to accomplish this.

The first time an application attempts to access user data, it will be redirected from the application to a login page or website where the user can grant permission for access.

OAuth works by decoupling authentication (verifying a user's identity) from authorization (determining what a user can access). When a user logs into an application like Google or Facebook and tries to access another application like a mobile app, OAuth kicks in.

The authorization server (like Google or Facebook) will authenticate the user and ask for their consent to share data with the other application.

If consent is granted, the authorization server issues an access token to the client application, which can access the user's data or make API calls on their behalf. These access tokens have limited lifetimes and scopes to reduce security risks.

(Source: https://cloudsundial.com/salesforce-oauth-flows)

The key points of the flow:

  1. The user logs into an application (like Google or Facebook) and grants access to another application (like a mobile app).
  2. The authorization server (like Google or Facebook) authenticates the user and asks for consent.
  3. If consent is granted, the authorization server issues an access token to the client application.
  4. The client application can then access data/make API calls on behalf of the user.
  5. Access tokens have a limited lifetime and scope to minimize security risks.

Why You Should be Using OAuth?

OAuth provides many benefits, including an improved user experience, increased security, easy implementation, revocable access, and scalability.

  • It is commonly used to authorize mobile apps, connect to services like social networks, enable single sign-on, give third parties limited data access, and create API access for web applications. Overall, OAuth allows for secure data sharing and access delegation between applications in today's connected world.
  • It enables users to give third-party applications limited, temporary access without sharing their account credentials (username/password). This means less user input is required from the user's side during registration.
  • It allows users more control over what information is shared with third parties and how long those third parties will be able to use that information.
  • OAuth provides a way for third-party applications to request authorization and access tokens from the user and then use those tokens to make API calls on behalf of the user. In this way, OAuth helps prevent unauthorized use of your API resources.
  • OAuth provides a more secure way for users to share information with trusted third-party apps without sharing their credentials (username and password). The user grants access by clicking an approve button within the app or website that wants access to the user's data. Once approved, the app or website can leverage the user's social network profile as it sees fit.

Examples of OAuth

OAuth is implemented in numerous real-world scenarios to enable secure access to resources. Below are some examples, along with simplified pseudo-code snippets:

1. Social Media Login (e.g., Facebook Login):

Many websites and apps allow users to log in or sign up using their social media accounts. OAuth is used to facilitate this.


# Client-side code

import oauth_library

# Redirect the user to the OAuth authentication provider (e.g., Facebook)

oauth_url = generate_oauth_url(client_id, redirect_uri, scope)


# Server-side code (after user authorizes)

authorization_code = get_authorization_code()

access_token = exchange_authorization_code_for_token(authorization_code)

user_info = get_user_info(access_token)

2. API Access (e.g., Google APIs):

Many services expose APIs that third-party applications can use. OAuth is employed to ensure secure access to these APIs.


# Client-side code

import oauth_library

# Redirect the user to the OAuth provider (e.g., Google)

oauth_url = generate_oauth_url(client_id, redirect_uri, scope)


# Server-side code (after user authorizes)

authorization_code = get_authorization_code()

access_token = exchange_authorization_code_for_token(authorization_code)

# Use the access token to make API requests

response = make_api_request(api_endpoint, access_token)

3. Single Sign-On (SSO):

OAuth is used for SSO solutions where a user logs in once and gains access to multiple related services without repeated logins.


# Client-side code

import oauth_library

# Redirect the user to the OAuth provider (e.g., SSO server)

oauth_url = generate_oauth_url(client_id, redirect_uri, scope)


# Server-side code (after user authorizes)

authorization_code = get_authorization_code()

access_token = exchange_authorization_code_for_token(authorization_code)

# Use the access token for SSO across multiple services

4. Mobile App Permissions (e.g., Twitter API):

Mobile apps often use OAuth to request specific permissions for posting on behalf of users or accessing their data.


# Mobile app code

import oauth_library

# Request user authorization

oauth_url = generate_oauth_url(client_id, redirect_uri, scope)


# After user authorizes, receive callback with authorization code

authorization_code = receiveCallbackWithCode()

# Exchange the code for an access token

access_token = exchange_authorization_code_for_token(authorization_code)

# Use the access token to post tweets or access user data

These pseudo-code snippets illustrate the common steps involved in OAuth flows. In actual implementations, you would use OAuth libraries or SDKs provided by the specific identity provider (e.g., Facebook, Google, Twitter) for handling the OAuth interactions.


So that's what OAuth is all about. While authentication is still a significant issue, OAuth has helped make using APIs a smoother and safer experience for developers and users. With all these new developments, we may have open data AND truly secure applications one day! We can only hope.

While the term OAuth can seem intimidating, it is easy to understand once you know the basics. The guide above taught you about the authentication process, when using OAuth is recommended, and more. Ultimately, it would help if you now had a greater understanding of how OAuth works and why it's essential to digital security.

OAuth offers more security, ease of use, and straightforward app integration. It's less cumbersome than a username and password approach to authentication, it is more consistent and versatile than using a developer API key, and it is easier for users to enroll than standard two-factor authentication. OAuth is the answer to unlocking all these benefits across any service or API that implements it.