Feature request: Add support for middlewares in event handler

[BVMiko]

Is your feature request related to a problem? Please describe.
Event handlers (specifically ApiGatewayResolver) are incompatible with middleware decorators. The lambda_handler_decorator is almost exactly what would be needed, except for the function signature.

Describe the solution you'd like
I'd like to be able to add middleware when using a router, and for the middleware to have access to the processed event:

@router_decorator
def db_middleware(handler, router, **kwargs):
    db = router.current_event.get_query_string_value(name="dbname", default_value='default_value')
    return handler(db=db, **kwargs)
    
@router.get("/users")
@db_middleware(router=router)
def get_users(db, foo) -> Dict:
    pagination_limit = router.current_event.get_query_string_value(name="limit", default_value=10)
    return {"pagination_limit": pagination_limit, "db": db}

Describe alternatives you've considered
Using a regular lambda_handler_decorator outside of the router.get is executed even when the router isn't called. The decorator wrapper could be stored in individual project code, but since it's so similar to the existing one and would be useful for any router usage, it makes sense to consider it for the aws-lambda-powertools library.

Additional context

[heitorlessa]

Hey @BVMiko - thanks for opening this feature request.

Perhaps a generic middleware factory decorator for any Python function with an arbitrary number of args, kwargs?

That would help make it more explicit so we have one for Lambda and for any function - it also makes it easier to preserve types and function signature (ParamSpec is only supported in later Python versions)

It's something I wanted to do for a long time but couldn't prioritise earlier

Thanks a lot btw!

[theNoobExpert]

@heitorlessa Here is what would make sense for middleware :
Defining middleware :

        def auth_middleware(app, handler):

        ### auth logic here ###

        setattr(app.current_event, "user", user_obj) # or app.current_event.extras["user"] = user_obj - a well defined place through which extra information can be passed on to routes.

        return handler()  # I haven't seen the code base so I don't know how difficult/easy it would be to implement this`

Registering middleware :

app.register_middleware(auth_middleware)

[heitorlessa]

Thanks a lot @karanhere3962 -- that's similar to FastAPI.

As this would run for every request, what's the UX you have in mind for a middleware that only runs on a given path?

Example:

• Register as part of route definition: @app.get("/path", middlewares=[]
• Register anywhere else: app.include_middleware(middleware, route="/path")

The details are important so we keep maintenance and extensibility at heart to follow our tenets.

Any other ideas would be great.

Cc @marcioemiranda who proposed this in the early days

[theNoobExpert]

Both the options that you have given seem great.