feat: allow running review app to validate PR from external contribution

* configure authentication layer on review application

apps/reviewapp.py

@@ -1,11 +1,26 @@
+"""
+This is a simple application to help our team to review contribution.
+
+>>> python apps/reviewapp.py
+
+Runs this application in public and requires authentication.
+
+>>> export HOST=0.0.0.0; export BASICAUTH=admin:admin; python apps/reviewapp.py
+"""
+import base64
 import os
+import time
 
 import uvicorn
 from fastapi.responses import HTMLResponse
-from fastapi import FastAPI, Response
+from fastapi import FastAPI, status
 
 import streamsync.serve
 
+HOST = os.getenv('HOST', 'localhost')
+PORT = int(os.getenv('PORT', '8000'))
+print(f"listen on {HOST}:{PORT}")
+
 
 def app_path(app_name: str) -> str:
     return os.path.join(os.path.dirname(__file__), app_name)
@@ -36,8 +51,65 @@ async def init():
         </ul>
         """, status_code=200)
 
+
+
+@root_asgi_app.middleware("http")
+async def valid_authentication(request, call_next):
+    """
+    Secures access to the review application using basic auth
+
+    The username and password is stored in the BASICAUTH environment variable.
+    The authentication process is sequential and when it's wrong it take one second to try again. This protection
+    is sufficient to limit brute force attack.
+    """
+    if HOST == 'localhost':
+        """
+        Locally, you can launch the review application without needing to authenticate.
+        
+        The application bypass the authentication middleware.
+        """
+        return await call_next(request)
+
+    _auth = request.headers.get('Authorization')
+    if not check_permission(_auth):
+        return HTMLResponse("", status.HTTP_401_UNAUTHORIZED, {"WWW-Authenticate": "Basic"})
+    return await call_next(request)
+
+
+def check_permission(auth) -> bool:
+    """
+    Secures access to the review application using basic auth
+
+    >>> is_valid_token = check_permission('Basic dXNlcm5hbWU6cGFzc3dvcmQ=')
+    """
+    if auth is None:
+        return False
+
+    scheme, data = (auth or ' ').split(' ', 1)
+    if scheme != 'Basic':
+        return False
+
+    username, password = base64.b64decode(data).decode().split(':', 1)
+    basicauth = os.getenv('BASICAUTH')
+    if auth is None:
+        raise ValueError('BASICAUTH environment variable is not set')
+
+    basicauth_part = basicauth.split(':')
+    if len(basicauth_part) != 2:
+        raise ValueError('BASICAUTH environment variable is not set')
+
+    basicauth_username, basicauth_password = basicauth_part
+
+    time.sleep(1)
+    if username == basicauth_username and password == basicauth_password:
+        return True
+    else:
+        time.sleep(1)
+        return False
+
+
 uvicorn.run(root_asgi_app,
-    host="0.0.0.0",
-    port=os.getenv('PORT', 8000),
+    host=HOST,
+    port=PORT,
     log_level="warning",
     ws_max_size=streamsync.serve.MAX_WEBSOCKET_MESSAGE_SIZE)