feat: restrict backend Container App to private access in WAF deployment

When enablePrivateNetworking (WAF mode) is active:
- Set Container App Environment to internal with public access disabled
- Set Container App ingress to internal (not externally accessible)
- Frontend Python server proxies /api/* requests to backend over VNet
- /config endpoint returns same-origin /api URL in WAF mode
- Non-WAF deployments remain unchanged (direct public API access)

Resolves AB#39249

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: Prajwal-Microsoft

docs/images/readme/1.png

@@ -1142,8 +1142,8 @@ module containerAppEnvironment 'br/public:avm/res/app/managed-environment:0.11.2
     tags: tags
     enableTelemetry: enableTelemetry
     // WAF aligned configuration for Private Networking
-    publicNetworkAccess: 'Enabled' // Always enabling the publicNetworkAccess for Container App Environment
-    internal: false //  Must be false when publicNetworkAccess is'Enabled'
+    publicNetworkAccess: enablePrivateNetworking ? 'Disabled' : 'Enabled'
+    internal: enablePrivateNetworking ? true : false
     infrastructureSubnetResourceId: enablePrivateNetworking ? virtualNetwork.?outputs.?containerSubnetResourceId : null
     // WAF aligned configuration for Monitoring
     appLogsConfiguration: enableMonitoring
@@ -1191,7 +1191,7 @@ module containerApp 'br/public:avm/res/app/container-app:0.18.1' = {
     environmentResourceId: containerAppEnvironment.outputs.resourceId
     managedIdentities: { userAssignedResourceIds: [userAssignedIdentity.outputs.resourceId] }
     ingressTargetPort: 8000
-    ingressExternal: true
+    ingressExternal: enablePrivateNetworking ? false : true
     activeRevisionsMode: 'Single'
     corsPolicy: {
       allowedOrigins: [
@@ -1399,7 +1399,7 @@ module containerAppMcp 'br/public:avm/res/app/container-app:0.18.1' = {
     environmentResourceId: containerAppEnvironment.outputs.resourceId
     managedIdentities: { userAssignedResourceIds: [userAssignedIdentity.outputs.resourceId] }
     ingressTargetPort: 9000
-    ingressExternal: true
+    ingressExternal: enablePrivateNetworking ? false : true
     activeRevisionsMode: 'Single'
     corsPolicy: {
       allowedOrigins: [
@@ -1531,6 +1531,7 @@ module webSite 'modules/web-sites.bicep' = {
           WEBSITES_PORT: '3000'
           WEBSITES_CONTAINER_START_TIME_LIMIT: '1800' // 30 minutes, adjust as needed
           BACKEND_API_URL: 'https://${containerApp.outputs.fqdn}'
+          PROXY_API_REQUESTS: enablePrivateNetworking ? 'true' : 'false'
           AUTH_ENABLED: 'false'
         }
         // WAF aligned configuration for Monitoring

docs/images/readme/2.png

@@ -1140,8 +1140,8 @@ module containerAppEnvironment 'br/public:avm/res/app/managed-environment:0.11.2
     tags: tags
     enableTelemetry: enableTelemetry
     // WAF aligned configuration for Private Networking
-    publicNetworkAccess: 'Enabled' // Always enabling the publicNetworkAccess for Container App Environment
-    internal: false //  Must be false when publicNetworkAccess is'Enabled'
+    publicNetworkAccess: enablePrivateNetworking ? 'Disabled' : 'Enabled'
+    internal: enablePrivateNetworking ? true : false
     infrastructureSubnetResourceId: enablePrivateNetworking ? virtualNetwork.?outputs.?containerSubnetResourceId : null
     // WAF aligned configuration for Monitoring
     appLogsConfiguration: enableMonitoring
@@ -1218,7 +1218,7 @@ module containerApp 'br/public:avm/res/app/container-app:0.18.1' = {
     environmentResourceId: containerAppEnvironment.outputs.resourceId
     managedIdentities: { userAssignedResourceIds: [userAssignedIdentity.outputs.resourceId] }
     ingressTargetPort: 8000
-    ingressExternal: true
+    ingressExternal: enablePrivateNetworking ? false : true
     activeRevisionsMode: 'Single'
     corsPolicy: {
       allowedOrigins: [
@@ -1441,7 +1441,7 @@ module containerAppMcp 'br/public:avm/res/app/container-app:0.18.1' = {
     environmentResourceId: containerAppEnvironment.outputs.resourceId
     managedIdentities: { userAssignedResourceIds: [userAssignedIdentity.outputs.resourceId] }
     ingressTargetPort: 9000
-    ingressExternal: true
+    ingressExternal: enablePrivateNetworking ? false : true
     activeRevisionsMode: 'Single'
     corsPolicy: {
       allowedOrigins: [
@@ -1582,6 +1582,7 @@ module webSite 'modules/web-sites.bicep' = {
           WEBSITES_PORT: '8000'
           //WEBSITES_CONTAINER_START_TIME_LIMIT: '1800' // 30 minutes, adjust as needed
           BACKEND_API_URL: 'https://${containerApp.outputs.fqdn}'
+          PROXY_API_REQUESTS: enablePrivateNetworking ? 'true' : 'false'
           AUTH_ENABLED: 'false'
           ENABLE_ORYX_BUILD: 'True'
         }

infra/main.bicep

@@ -1,10 +1,11 @@
 import os
 
+import httpx
 import uvicorn
 from dotenv import load_dotenv
-from fastapi import FastAPI
+from fastapi import FastAPI, Request
 from fastapi.middleware.cors import CORSMiddleware
-from fastapi.responses import FileResponse
+from fastapi.responses import FileResponse, StreamingResponse
 from fastapi.staticfiles import StaticFiles
 
 # Load environment variables from .env file
@@ -23,6 +24,10 @@
 BUILD_DIR = os.path.join(os.path.dirname(__file__), "build")
 INDEX_HTML = os.path.join(BUILD_DIR, "index.html")
 
+# Proxy configuration for WAF/private networking deployments
+PROXY_API_REQUESTS = os.getenv("PROXY_API_REQUESTS", "false").lower() == "true"
+BACKEND_API_URL = os.getenv("BACKEND_API_URL", "http://localhost:8000")
+
 # Serve static files from build directory
 app.mount(
     "/assets", StaticFiles(directory=os.path.join(BUILD_DIR, "assets")), name="assets"
@@ -36,17 +41,59 @@ async def serve_index():
 
 @app.get("/config")
 async def get_config():
-    backend_url = os.getenv("BACKEND_API_URL", "http://localhost:8000")
     auth_enabled = os.getenv("AUTH_ENABLED", "false")
-    backend_url = backend_url + "/api"
+
+    if PROXY_API_REQUESTS:
+        # WAF mode: frontend proxies API calls, so tell browser to use same origin
+        api_url = "/api"
+    else:
+        # Non-WAF mode: browser calls backend directly
+        backend_url = os.getenv("BACKEND_API_URL", "http://localhost:8000")
+        api_url = backend_url + "/api"
 
     config = {
-        "API_URL": backend_url,
+        "API_URL": api_url,
         "ENABLE_AUTH": auth_enabled,
     }
     return config
 
 
+@app.get("/health")
+async def health():
+    return {"status": "healthy"}
+
+
+# API proxy routes for WAF/private networking deployments
+if PROXY_API_REQUESTS:
+
+    @app.api_route("/api/{path:path}", methods=["GET", "POST", "PUT", "DELETE", "PATCH"])
+    async def proxy_api(request: Request, path: str):
+        """Proxy API requests to the private backend over VNet."""
+        target_url = f"{BACKEND_API_URL}/api/{path}"
+        query_string = str(request.query_params)
+        if query_string:
+            target_url = f"{target_url}?{query_string}"
+
+        headers = dict(request.headers)
+        headers.pop("host", None)
+
+        body = await request.body()
+
+        async with httpx.AsyncClient(timeout=300.0) as client:
+            response = await client.request(
+                method=request.method,
+                url=target_url,
+                headers=headers,
+                content=body,
+            )
+
+        return StreamingResponse(
+            iter([response.content]),
+            status_code=response.status_code,
+            headers=dict(response.headers),
+        )
+
+
 @app.get("/{full_path:path}")
 async def serve_app(full_path: str):
     # Remediation: normalize and check containment before serving

infra/main_custom.bicep

@@ -1,6 +1,7 @@
 fastapi
 uvicorn[standard]
 # uvicorn removed and added above to allow websocket support
+httpx
 jinja2
 azure-identity
 python-dotenv