Add ":servlet:spring-boot:java:oauth2:resource-server:opaque"

servlet/spring-boot/java/oauth2/resource-server/opaque/README.adoc

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+= OAuth 2.0 Resource Server Sample
+
+This sample demonstrates integrating Resource Server with a mock Authorization Server, though it can be modified to integrate
+with your favorite Authorization Server.
+
+With it, you can run the integration tests or run the application as a stand-alone service to explore how you can
+secure your own service with OAuth 2.0 Opaque Bearer Tokens using Spring Security.
+
+== 1. Running the tests
+
+To run the tests, do:
+
+```bash
+./gradlew integrationTest
+```
+
+Or import the project into your IDE and run `OAuth2ResourceServerApplicationTests` from there.
+
+=== What is it doing?
+
+By default, the tests are pointing at a mock Authorization Server instance.
+
+The tests are configured with a set of hard-coded tokens originally obtained from the mock Authorization Server,
+and each makes a query to the Resource Server with their corresponding token.
+
+The Resource Server subsquently verifies with the Authorization Server and authorizes the request, returning the phrase
+
+```bash
+Hello, subject!
+```
+
+where "subject" is the value of the `sub` field in the JWT returned by the Authorization Server.
+
+== 2. Running the app
+
+To run as a stand-alone application, do:
+
+```bash
+./gradlew bootRun
+```
+
+Or import the project into your IDE and run `OAuth2ResourceServerApplication` from there.
+
+Once it is up, you can use the following token:
+
+```bash
+export TOKEN=00ed5855-1869-47a0-b0c9-0f3ce520aee7
+```
+
+And then make this request:
+
+```bash
+curl -H "Authorization: Bearer $TOKEN" localhost:8080
+```
+
+Which will respond with the phrase:
+
+```bash
+Hello, subject!
+```
+
+where `subject` is the value of the `sub` field in the JWT returned by the Authorization Server.
+
+Or this:
+
+```bash
+export TOKEN=b43d1500-c405-4dc9-b9c9-6cfd966c34c9
+
+curl -H "Authorization: Bearer $TOKEN" localhost:8080/message
+```
+
+Will respond with:
+
+```bash
+secret message
+```
+
+== 2. Testing against other Authorization Servers
+
+_In order to use this sample, your Authorization Server must support Opaque Tokens and the Introspection Endpoint.
+
+To change the sample to point at your Authorization Server, simply find this property in the `application.yml`:
+
+```yaml
+spring:
+  security:
+    oauth2:
+      resourceserver:
+        opaque:
+          introspection-uri: ${mockwebserver.url}/introspect
+          introspection-client-id: client
+          introspection-client-secret: secret
+```
+
+And change the property to your Authorization Server's Introspection endpoint, including its client id and secret:
+
+```yaml
+spring:
+  security:
+    oauth2:
+      resourceserver:
+        opaque:
+          introspection-uri: ${mockwebserver.url}/introspect
+```
+
+And then you can run the app the same as before:
+
+```bash
+./gradlew bootRun
+```
+
+Make sure to obtain valid tokens from your Authorization Server in order to play with the sample Resource Server.
+To use the `/` endpoint, any valid token from your Authorization Server will do.
+To use the `/message` endpoint, the token should have the `message:read` scope.