> For the complete documentation index, see [llms.txt](https://andifalk.gitbook.io/oauth-2.1-and-openid-connect-for-java-developers/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://andifalk.gitbook.io/oauth-2.1-and-openid-connect-for-java-developers/introduction/architecture.md).

# Sample Application Architecture

## Architecture

We will extend the existing two microservices to use federated authentication based on OAuth 2.1 and OpenID Connect (OIDC).

* **OpenID Connect (OIDC) Identity Provider**: This is central identity provider for single sign on which holds all users with their credentials
* **OAuth2/OIDC Resource Server (product-initial)**: The backend microservice providing product data (the OAuth2/OIDC resource server)
* **OAuth2/OIDC Client (ui-initial)**: The frontend UI microservice consuming the products (the OAuth2/OIDC client)

![Architecture](https://1133389852-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FbiwuDXJt0wISJ2RSFyii%2Fuploads%2Fgit-blob-b65ba07489f69e667da8d15100212d49595f7b96%2Farchitecture.png?alt=media)

## Configuration

These microservices are configured to be reachable via the following URL addresses (Port 8080 is the default port in spring boot).

Service URLs:

| Service                        | URL                            |
| ------------------------------ | ------------------------------ |
| OIDC Identity Provider         | <http://localhost:9000>        |
| Client (UI)                    | <http://localhost:9095/client> |
| Resource Server (Products API) | <http://localhost:9090/server> |

## Project contents

After importing the project into your IDE you should see a project structure like in the following picture. Here the VS Code project is shown, it may look different in other IDE's.

![Project Structure](https://1133389852-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FbiwuDXJt0wISJ2RSFyii%2Fuploads%2Fgit-blob-ce2531b36f35ba1e6e07a01a7574217c51ff8163%2Fproject_structure.png?alt=media)

The main contents for this workshop consist of the following directories:

* **intro-labs**: In the sub-directory *auth-code-in-action* you find a demo application that illustrates the OAuth 2 authorization code grant flow in details. Here you can follow all the subsequent steps happening during this protocol flow variant.\
  In the sub-directory *oauth\_grants* you get instructions on how to try different OAuth 2 authorization grant flows yourself with different tools like *postman*, *curl* and *httpie*.
* **labs**: In this directory you find the workshop lab parts.
  * initial: This will be the starting point to implement code as part of this workshop
    * product: This is the provided sample product server microservice
    * ui: This is the provided sample product ui client microservice
  * solution: This is the reference solution for this workshop (please do NOT look into this now)
    * product: This is the reference solution of a OAuth2/OIDC product server microservice
    * ui: This is the reference solution of a OAuth2/OIDC product ui client microservice

> **Info:** You can find more information on building OAuth 2.0/OIDC secured microservices with spring in [Spring Boot Reference Documentation](https://docs.spring.io/spring-boot/docs/current/reference/htmlsingle/#boot-features-security-oauth2) and in [Spring Security Reference Documentation](https://docs.spring.io/spring-security/site/docs/current/reference/htmlsingle/#oauth2)

So let's start with implementing the server side: The API (resource server).