diff --git a/src/main/kotlin/nmcp/NmcpAggregation.kt b/src/main/kotlin/nmcp/NmcpAggregation.kt
index 5db5ead..9e6d4f3 100644
--- a/src/main/kotlin/nmcp/NmcpAggregation.kt
+++ b/src/main/kotlin/nmcp/NmcpAggregation.kt
@@ -3,16 +3,19 @@ package nmcp
 import org.gradle.api.Project
 import org.gradle.api.artifacts.Configuration
 import org.gradle.api.provider.Property
+import javax.inject.Inject
 
-class NmcpAggregation(
+
+abstract class NmcpAggregation @Inject constructor(
     private val configuration: Configuration,
     private val project: Project,
-    val username: Property<String>,
-    val password: Property<String>,
-    val publicationType: Property<String>,
-    val publicationName: Property<String>,
-    val endpoint: Property<String>,
     ) {
+    abstract val username: Property<String>
+    abstract val password: Property<String>
+    abstract val publicationType: Property<String>
+    abstract val publicationName: Property<String>
+    abstract val endpoint: Property<String>
+
     fun project(path: String) {
         project.dependencies.add(configuration.name, project.dependencies.project(mapOf("path" to  path)))
     }
diff --git a/src/main/kotlin/nmcp/NmcpExtension.kt b/src/main/kotlin/nmcp/NmcpExtension.kt
index 55b8a25..420c4ce 100644
--- a/src/main/kotlin/nmcp/NmcpExtension.kt
+++ b/src/main/kotlin/nmcp/NmcpExtension.kt
@@ -6,7 +6,7 @@ import org.gradle.api.publish.PublishingExtension
 import org.gradle.api.tasks.bundling.Zip
 import org.gradle.configurationcache.extensions.capitalized
 
-class NmcpExtension(private val project: Project) {
+open class NmcpExtension(private val project: Project) {
     private var mavenPublishFound = false
     private val publishAllPublicationsToCentralPortal = project.tasks.register("publishAllPublicationsToCentralPortal")
 
@@ -84,13 +84,7 @@ class NmcpExtension(private val project: Project) {
     }
 
     private fun publishInternal(publicationName: String?, action: Action<NmcpSpec>) {
-        val spec = NmcpSpec(
-            project.objects.property(String::class.java),
-            project.objects.property(String::class.java),
-            project.objects.property(String::class.java),
-            project.objects.property(String::class.java),
-            project.objects.property(String::class.java),
-        )
+        val spec = project.objects.newInstance(NmcpSpec::class.java)
         action.execute(spec)
 
         project.plugins.withId("maven-publish") {
@@ -139,15 +133,7 @@ class NmcpExtension(private val project: Project) {
             it.configureAttributes(project)
         }
 
-        val aggregation = NmcpAggregation(
-            configuration,
-            project,
-            project.objects.property(String::class.java),
-            project.objects.property(String::class.java),
-            project.objects.property(String::class.java),
-            project.objects.property(String::class.java),
-            project.objects.property(String::class.java),
-        )
+        val aggregation = project.objects.newInstance(NmcpAggregation::class.java, configuration, project)
 
         action.execute(aggregation)
 
@@ -184,13 +170,7 @@ class NmcpExtension(private val project: Project) {
             "publishAllProjectsProbablyBreakingProjectIsolation() must be called from root project"
         }
 
-        val spec = NmcpSpec(
-            project.objects.property(String::class.java),
-            project.objects.property(String::class.java),
-            project.objects.property(String::class.java),
-            project.objects.property(String::class.java),
-            project.objects.property(String::class.java),
-        )
+        val spec = project.objects.newInstance(NmcpSpec::class.java)
         action.execute(spec)
 
         publishAggregation { aggregation ->
diff --git a/src/main/kotlin/nmcp/NmcpPlugin.kt b/src/main/kotlin/nmcp/NmcpPlugin.kt
index 8725880..8666bbd 100644
--- a/src/main/kotlin/nmcp/NmcpPlugin.kt
+++ b/src/main/kotlin/nmcp/NmcpPlugin.kt
@@ -28,6 +28,6 @@ class NmcpPlugin: Plugin<Project> {
 
             it.configureAttributes(target)
         }
-        target.extensions.add("nmcp", NmcpExtension(target))
+        target.extensions.create("nmcp", NmcpExtension::class.java, target)
     }
 }
\ No newline at end of file
diff --git a/src/main/kotlin/nmcp/NmcpSpec.kt b/src/main/kotlin/nmcp/NmcpSpec.kt
index 3e1f41e..6b56a5e 100644
--- a/src/main/kotlin/nmcp/NmcpSpec.kt
+++ b/src/main/kotlin/nmcp/NmcpSpec.kt
@@ -2,10 +2,10 @@ package nmcp
 
 import org.gradle.api.provider.Property
 
-class NmcpSpec(
-    val username: Property<String>,
-    val password: Property<String>,
-    val publicationType: Property<String>,
-    val publicationName: Property<String>,
-    val endpoint: Property<String>,
-)
\ No newline at end of file
+abstract class NmcpSpec {
+    abstract val username: Property<String>
+    abstract val password: Property<String>
+    abstract val publicationType: Property<String>
+    abstract val publicationName: Property<String>
+    abstract val endpoint: Property<String>
+}
\ No newline at end of file