1. Introduction

In this short tutorial, we’ll briefly discuss OAuth 2 grant types.

2. OAuth 2 Grant Types

An OAuth 2 grant type is a method defined by the OAuth 2.0 authorization framework that allows a client application to obtain an access token.

Various applications may exist, and the choice of OAuth grant type depends on the client application’s nature and the specific use case. For instance, there could be a server-side web application developed in Java or PHP, and a particular OAuth grant type is specifically suited for these types of applications. Server-side scripts without any user interface can utilize a different OAuth grant type to obtain an access token, tailored to their specific requirements.

A client application could also take the form of a single-page JavaScript application or a native mobile application, such as those running on iOS or Android. Since there are various types of applications, and some may be less secure than others, different OAuth grant types were designed to address these variations. Each grant type is used to obtain an access token in a slightly different manner, depending on the application’s security level and requirements. Following are the examples of grant types suited for the application types:

Application type	Grant type
Server side web application	Authorization code
Server side script with no UI	Client Credentials
JavaScript Single Page application	PKCE Enhanced Authorization Code
Mobile native application	Authorization code, PKCE Enhanced Authorization Code
Device	Device code

A client application can also be a single-page JavaScript application or a native mobile app, such as one running on iOS or Android. Additionally, there are applications that run on devices like TVs or gaming consoles, such as PlayStation that are unable to open a browser window or execute scripts on the server side. Since there are various types of applications, and some may be less secure than others, different OAuth grant types have been designed to address these differences.

Each grant type is used to obtain an access token in a slightly different way. For instance, the Authorization Code grant type is commonly used in server-side web applications as well as mobile applications. Another example is the Client Credentials grant type, which is often used in server-side applications that lack a user interface and are not directly accessible to end users. There is also an extension of the Authorization Code grant type called the Proof Key for Code Exchange (PKCE) enhanced authorization code. This version is designed for applications that cannot securely store their client credentials, such as single-page or mobile applications. There are various types of client applications, each with different needs and varying capacities to protect client credentials. Consequently, some OAuth grant types are more suitable for specific applications than others.

There is also a grant type known as the Refresh Token grant type, which is used to exchange a refresh token for a new access token. A refresh token is obtained along with an access token. This grant type enables client applications to refresh an expired access token without further interaction from the end user. If the access token expires, the application can use the refresh token to obtain a new access token and continue interacting with the server-side API seamlessly.

Some grant types have been deprecated. However, you might still encounter them when working with legacy projects. One such grant type is the Implicit Grant, commonly used with JavaScript or mobile applications. In this case, the access token is returned immediately without requiring an additional authorization code exchange. One such grant type is the Implicit Grant, commonly used with JavaScript or mobile applications. In this case, the access token is returned immediately without requiring an additional authorization code exchange.

Another example of a deprecated grant type that is no longer recommended is the Password Grant Type. This grant type, which is still seen in various applications, allows for exchanging user credentials directly for an access token. However, since this grant type requires the client application to collect and transmit the user’s password to the authorization server, it is no longer recommended for use.

3. Summary

Following is the summary of OAuth 2 grant types:

• Authorization Code Grant: Used by server-side applications to obtain an access token. It involves a two-step process where an authorization code is first obtained and then exchanged for an access token.
• Implicit Grant: Used by client-side applications (e.g., single-page apps) where the access token is returned directly without an intermediate authorization code. This method is less secure and is now generally deprecated.
• Resource Owner Password Credentials Grant: Used when the user’s credentials are directly provided to the client application, which then exchanges them for an access token. This grant type is also deprecated in favor of more secure methods.
• Client Credentials Grant: Used by applications to obtain an access token based on their own credentials, not on behalf of a user. This is often used for server-to-server communication.
• Refresh Token Grant: Allows an application to obtain a new access token by using a refresh token that was issued along with the original access token, without requiring the user to re-authenticate.

4. Conclusion

In conclusion, understanding the various OAuth 2 grant types is crucial for implementing secure and efficient authentication and authorization processes in your applications. Each grant type is tailored to specific scenarios, whether it’s for web applications, mobile apps, or server-to-server interactions. By choosing the appropriate grant type based on your application’s needs and security requirements, you can ensure a smooth user experience while maintaining robust security practices. As you continue to explore OAuth 2.0, you’ll gain a deeper appreciation for how these grant types work together to protect user data and facilitate secure access to resources.