Handling Authorization in an OAuth 2.0 Spring Boot Application When Interacting with a Third-Party Service

Question

I have experience implementing various OAuth 2.0 scenarios involving both clients and resource servers, including calls from non-secured services to my client and vice versa. However, I've encountered a situation that has left me a bit puzzled regarding the OAuth 2.0 authorization process, specifically about when and where the authorization prompt should appear.

Scenario: I have a Spring Boot application, which I'll refer to as Service1, set up with OAuth 2.0 client dependencies. This service includes a login form that uses Google as the identity provider. My goal is to have Service1 send a request to another service, which we'll call Service2, that is not secured with OAuth 2.0. I'm uncertain about how the authorization flow should proceed in this case and where the authorization should occur.

Previously, I have successfully implemented a scenario involving two Spring Boot services: one acting as a Resource Server and the other as an OAuth 2.0 client. In this setup, when attempting to access an endpoint that retrieves data from the Resource Server, an authorization window pops up. After logging in, the data is successfully returned.

What I Want to Achieve: I aim to replicate a similar flow as described above, but with a twist. Here's a conceptual diagram of what I'm envisioning:

Instead of using the specific "SnapStore" and "Print Service" mentioned in the diagram, I intend to substitute them with dummy services for experimentation purposes. My primary question revolves around the necessity of access tokens for service-to-service communication. Specifically, when I send a request from a dummy non-OAuth 2.0 service to an OAuth 2.0 secured service, I receive a 302 response along with an authorization link, which I then redirect.

Questions:

• How should the OAuth 2.0 authorization flow be handled in this scenario, especially considering the interaction with a non-secured third-party service (Service2)?
• Is my understanding correct that service-to-service communication requires access tokens, and if so, how should the redirection to the authorization link be managed appropriately in this context?

Any insights or guidance on how to properly set up and handle this authorization flow would be greatly appreciated.

Answer 1

In your scenario, Service1 acts as an OAuth 2.0 client and Service2 is a non-secured service. When Service1 needs to access Service2, the authorization flow typically depends on the requirements of Service2 and the nature of the interaction between the services.

Here's how you could handle the OAuth 2.0 authorization flow in this scenario:

1. Interaction with Service2:

   • Since Service2 is not secured with OAuth 2.0, it does not require access tokens for authorization. Therefore, there's no need for Service1 to obtain an access token specifically for communicating with Service2.

2. Authorization Flow:

   • When Service1 needs to access resources from Service2, it can make HTTP requests directly to Service2 without involving OAuth 2.0 authorization. Service2 should handle these requests based on its own authentication and authorization mechanisms.

3. Handling Authorization Prompt:

   • Since Service1 is an OAuth 2.0 client, it might still need to prompt the user for authorization when accessing protected resources on behalf of the user. However, if Service1 is simply making internal requests to Service2 without involving user-specific data, there may be no need for an authorization prompt.

4. Handling Redirects:

   • If Service1 receives a 302 response along with an authorization link when accessing Service2, it indicates that Service2 requires some form of authentication or authorization. In this case, you need to handle the redirect appropriately. If Service2 requires OAuth 2.0 authorization, Service1 might need to redirect the user to the authorization server (e.g., Google) to obtain an access token before accessing Service2.

5. Service-to-Service Communication:

   • Service-to-service communication typically requires some form of authentication or authorization mechanism. However, it doesn't necessarily have to be OAuth 2.0. If Service2 does not require OAuth 2.0 authorization, Service1 can directly communicate with Service2 without involving access tokens.

In summary, in scenarios where Service1 needs to access a non-secured service (Service2), you can bypass the OAuth 2.0 authorization flow and make direct HTTP requests. However, if Service2 requires authentication or authorization, you need to handle it according to its requirements, which may involve redirects and user authorization prompts.