Add Dockerfile and main.go for OPA with NATS plugin integration

Introduce a new Dockerfile for building the OPA binary with the NATS store plugin. The Dockerfile includes multi-stage builds for dependency management and a non-root user setup. Additionally, add main.go to implement the OPA runtime with the NATS plugin, enhancing the project's capabilities. Update docker-compose.yaml to reference the new Dockerfile and adjust the command for running the OPA server.

Author: omer9564

Dockerfile

@@ -0,0 +1,34 @@
+FROM --platform=$BUILDPLATFORM golang:1.23-alpine AS builder
+
+ARG TARGETOS
+ARG TARGETARCH
+
+WORKDIR /app
+
+# Copy go.mod and go.sum for dependency caching
+COPY go.mod go.sum ./
+
+# Download dependencies
+RUN go mod download
+
+# Copy the entire source code
+COPY . .
+
+# Build the custom OPA binary with natsstore plugin
+RUN CGO_ENABLED=0 GOOS=$TARGETOS GOARCH=$TARGETARCH go build -o opa ./cmd/opa-nats
+
+FROM alpine:latest
+
+# Install ca-certificates for TLS connections
+RUN apk --no-cache add ca-certificates
+
+# Create non-root user
+RUN adduser -D -s /bin/sh opa
+
+# Copy the built binary from builder stage
+COPY --from=builder /app/opa /usr/local/bin/opa
+
+# Switch to non-root user
+USER opa
+
+ENTRYPOINT ["opa"]

cmd/opa-nats/main.go

@@ -0,0 +1,18 @@
+package main
+
+import (
+	"log"
+
+	"github.com/open-policy-agent/opa/cmd"
+	"github.com/open-policy-agent/opa/v1/runtime"
+	natsstore "github.com/permitio/opa-nats/pkg/natsstore"
+)
+
+func main() {
+	pluginFactory := natsstore.NewPluginFactory()
+	runtime.RegisterPlugin(natsstore.PluginName, pluginFactory)
+
+	if err := cmd.RootCommand.Execute(); err != nil {
+		log.Fatalf("Failed to execute OPA runtime: %v", err)
+	}
+}

examples/handledpaths/Dockerfile

@@ -131,13 +131,13 @@ services:
   opa:
     build:
       context: ../../
-      dockerfile: examples/handledpaths/Dockerfile
-    container_name: opa-server
+      dockerfile: Dockerfile
     depends_on:
       nats:
         condition: service_healthy
       nats-setup:
         condition: service_completed_successfully
+    command: ["run", "--server", "--config-file=/config/config.yaml", "/policies", "--addr", "0.0.0.0:8181"]
     ports:
       - "8181:8181"
     volumes: