NodeJS store session in cache memory best practice

I need to build an architecture for a SaaS system, which will be separated to a few lambda functions on the backend, and one of them is a sign in / sign up service, which should verify user credentials and in case of a success create a session and return it to a user using a session cookie.
First of all, I thought of using a server so I can achieve a single entry point to the backend and will forward the requests to the lambdas endpoints.