I have a FastAPI application deployed as an Azure Web App (free tier). Locally, everything runs fine and all previous deployments on Azure too, but since I added a custom Middleware, I get "Internal Server Error". The logs of Azure don't really help me, too. 

from foodfusionai.redis_rate_limiting import get_user_identifier, get_user_type, get_rate_limit_rules, RedisRateLimitMiddleware

api_version = project_config['api']['version']
app = FastAPI(title=project_config['app']['title'], version=api_version)

app.add_middleware(
    CORSMiddleware,
    allow_origins=["*"],    # origins set in Azure Web App
    allow_credentials=True,
    allow_methods=["*"],  
    allow_headers=["*"]
)

rules, default_rule = get_rate_limit_rules()

# when I comment this, it works!
app.add_middleware(
    RedisRateLimitMiddleware,
    rate_limit_rules=rules,
    default_rule=default_rule,
    identifier_func=get_user_identifier,
    user_type_func=get_user_type,
    whitelist=["127.0.0.1"],   
    prefix="foodfusionai:ratelimit:"
)