How do you secure your APIs with OAuth tokens and scopes?

1 What is OAuth?

OAuth is a framework that enables clients to access protected resources on behalf of a resource owner, such as a user or a service. OAuth does not define how the clients authenticate themselves to the authorization server, but rather how they obtain and use access tokens to request resources from the API server. An access token is a string that represents the authorization granted to the client by the resource owner. The token can have an expiration time, a refresh mechanism, and a scope that limits the access to specific resources or actions. OAuth supports different flows or grant types, depending on the type of client and the level of trust between the parties involved. Some of the most common flows are authorization code, implicit, client credentials, and password.

2 How do scopes work?

Scopes are a way of defining and enforcing the boundaries of access for each token. They are essentially labels or identifiers that represent a set of permissions or actions that the client can perform with the token. For example, a scope can be read, write, delete, or admin. The resource owner can grant or deny scopes to the client when authorizing the token request, and the API server can check the scopes of the token when processing the resource request. Scopes can be predefined by the API server, or dynamically negotiated by the client and the authorization server. Scopes can also be hierarchical, meaning that a higher-level scope can imply lower-level scopes. For example, admin can include read and write.

3 Why use OAuth tokens and scopes?

Using OAuth tokens and scopes to secure your APIs offers several advantages. By decoupling the authentication and authorization processes, you can achieve more flexibility and interoperability between different systems and platforms. Additionally, you reduce the risk of credential leakage or theft, as clients don’t need to store or transmit the resource owner's credentials, but only use short-lived and revocable tokens. Furthermore, the user experience and control is enhanced, as the resource owner can grant or revoke access to specific resources or actions without compromising their account security or privacy. Moreover, it improves the performance and scalability of the API server, as token validation can be done locally or with a cache without requiring additional database queries or network calls.

4 What are the challenges of OAuth tokens and scopes?

Despite its advantages, OAuth tokens and scopes also present some challenges and limitations. For developers, these include increasing the complexity and overhead of API design and implementation, as well as potential security vulnerabilities and attacks if tokens are not properly protected, transmitted, or stored. Additionally, users must be educated on the scopes and terms of service of each client and authorization server, as well as consent to them. Furthermore, the compatibility and compliance of OAuth implementations may result in variations or deviations from the standard specifications or best practices.

5 How to implement OAuth tokens and scopes?

The implementation of OAuth tokens and scopes requires consideration of various factors such as the type of client, the type of flow, the type of token, and the type of scope. Generally, the steps involved include registering with the authorization server to obtain a client ID and a client secret (if applicable). The client then initiates the token request by redirecting the resource owner to the authorization server's endpoint, passing along the client ID, the redirect URI, the response type, and the requested scopes. After authenticating and obtaining consent for the requested scopes from the resource owner, the authorization server redirects them back to the client's redirect URI with an authorization code (if using the authorization code flow) or an access token (if using the implicit flow). The client then exchanges this authorization code for an access token (if using the authorization code flow) by sending a request to the authorization server's token endpoint. Upon receiving an access token (and optionally a refresh token) from the authorization server, along with its type, expiration time, and granted scopes, it can then be used to request resources from API server by sending it as a header or a parameter. Finally, if everything is valid, API server will return requested resources or an error message.

6 Here’s what else to consider

This is a space to share examples, stories, or insights that don’t fit into any of the previous sections. What else would you like to add?