Expose an example config.yaml over the registry's REST api

pom.xml

@@ -205,6 +205,7 @@
           <systemPropertyVariables>
             <java.util.logging.manager>org.jboss.logmanager.LogManager</java.util.logging.manager>
             <maven.home>${maven.home}</maven.home>
+            <quarkus.registry.expose.client.config.yaml>true</quarkus.registry.expose.client.config.yaml>
           </systemPropertyVariables>
         </configuration>
       </plugin>

src/main/java/io/quarkus/registry/app/ClientConfigYamlEndpoint.java

@@ -0,0 +1,59 @@
+package io.quarkus.registry.app;
+
+import java.io.IOException;
+import java.io.StringWriter;
+import java.io.Writer;
+
+import org.eclipse.microprofile.openapi.annotations.Operation;
+import org.eclipse.microprofile.openapi.annotations.tags.Tag;
+
+import io.quarkus.maven.dependency.ArtifactCoords;
+import io.quarkus.registry.app.maven.MavenConfig;
+import io.quarkus.registry.config.*;
+import io.quarkus.resteasy.reactive.server.EndpointDisabled;
+import jakarta.enterprise.context.ApplicationScoped;
+import jakarta.inject.Inject;
+import jakarta.ws.rs.GET;
+import jakarta.ws.rs.Path;
+import jakarta.ws.rs.Produces;
+import jakarta.ws.rs.core.MediaType;
+
+/**
+ * Exposes the Quarkus Registry Client configuration file on `/config.yaml`. This is only enabled if
+ * {@code quarkus.registry.expose.client.config.yaml} is set to {@code true}.
+ */
+@ApplicationScoped
+@Path("/client")
+@Tag(name = "Client", description = "Client related services")
+@EndpointDisabled(name = "quarkus.registry.expose.client.config.yaml", stringValue = "false", disableIfMissing = true)
+public class ClientConfigYamlEndpoint {
+
+    @Inject
+    MavenConfig mavenConfig;
+
+    @GET
+    @Path("/config.yaml")
+    @Produces(MediaType.TEXT_PLAIN)
+    @Operation(summary = "Example Quarkus Registry Client configuration file")
+    public String clientConfigYaml() throws IOException {
+        ArtifactCoords coords = ArtifactCoords
+                .fromString(mavenConfig.getRegistryGroupId() + ":quarkus-registry-descriptor::json:1.0-SNAPSHOT");
+        RegistryMavenRepoConfig mavenRepoConfig = RegistryMavenRepoConfig.builder().setUrl(mavenConfig.getRegistryUrl())
+                .build();
+        RegistryConfig registry = RegistryConfig.builder()
+                .setId(mavenConfig.getRegistryId())
+                .setUpdatePolicy("always")
+                .setDescriptor(
+                        RegistryDescriptorConfig.builder().setArtifact(coords))
+                .setMaven(
+                        RegistryMavenConfig.builder()
+                                .setRepository(mavenRepoConfig)
+                                .build())
+                .build();
+        RegistriesConfig registries = RegistriesConfig.builder().setRegistry(registry).build();
+        Writer resultWriter = new StringWriter();
+        RegistriesConfigMapperHelper.toYaml(registries, resultWriter);
+        return resultWriter.toString();
+    }
+
+}

src/test/java/io/quarkus/registry/app/services/ClientConfigurationFileTest.java

@@ -0,0 +1,34 @@
+package io.quarkus.registry.app.services;
+
+import static io.restassured.RestAssured.given;
+
+import org.hamcrest.Matchers;
+import org.junit.jupiter.api.Test;
+
+import io.quarkus.registry.app.BaseTest;
+import io.quarkus.registry.app.maven.MavenConfig;
+import io.quarkus.test.junit.QuarkusTest;
+import jakarta.inject.Inject;
+
+@QuarkusTest
+public class ClientConfigurationFileTest extends BaseTest {
+
+    @Inject
+    MavenConfig mavenConfig;
+
+    @Test
+    void getClientConfigurationYaml() {
+        given()
+                .get("/client/config.yaml")
+                .prettyPeek()
+                .then()
+                .contentType("text/plain")
+                .body(Matchers.containsString(
+                        """
+                                    maven:
+                                      repository:
+                                        url: "%1s"
+                                """.formatted(mavenConfig.getRegistryUrl())))
+                .statusCode(200);
+    }
+}