I hope this post fits in this community :)

I'm trying to wrap my head around how authentication works with micro services.

Say we have a system, with a frontend, that communicates with an API gateway, which in turn communicates with all the micro services.

As I understand it, we authenticate the client in the API gateway, and if we trust the client, the request are forwarded to the micro services.

However, what is stopping a malicious actor from bypassing the API gateway and communicating directly to the micro services ?

Do we solve this problem using a firewall, so only trusted traffic reaches the micro services ?

Or do we still have API keys between the API gateway and the micro services ?

Or is there a third way ? :)

All the articles I've read seem to assume, that we can trust all traffic entering the micro services