[cortesi]

It looks like the /stats endpoint consults the Redis database and returns processed data. If we're aggregating metrics externally, it would be more idiomatic for this to be totally stateless and just expose hot metrics - it's the aggregator's job to store and process the data. This can be quite painless using something like the Go Prometheus library.

Being tied to Redis is also not great. For instance, it looks like everything apart from the metrics could comfortably live in Google Cloud Storage if you had a backend for it. Cloud Storage really isn't an appropriate place to put frequently updated counters, though. So if I deployed AuthN, I would want to be able to ditch Redis.

I should stress, though, that these are quibbles. I think AuthN looks very nice, and the quibbles are cropping up because I'm trying to figure out if I can use it. :)

[cainlevy]

That all sounds like a direction I'd happily consider:

* Google Cloud Storage implementations for data interfaces

* Metrics interface with a Prometheus implementation (STATSD to follow)

* Redis-backed HLL metrics are optional

Feel free to open issues in the tracker if you reach that point!

[cortesi]

Good stuff.

I have one other bit of feedback on the architecture, and I realise that this one might be too different from where AuthN is currently. I see that there are a small number of API endpoints that you've marked "public" that users are meant to be able to reach. In practice, the user's POSTs would always be terminated upstream from the AuthN server itself, either at a gateway or by just relaying the requests through from the front-end servers themselves. A service that's part public/part private is much more perilous than a service that is one or the other. All things considered, these public endpoints seem like a very minor convenience to the integrator. I would just make the AuthN API private, and ask users to implement the public endpoints themselves by making requests to the AuthN API.

If you DID make all endpoints private, you're no longer tied to HTTP, and you have a nice opportunity to use GRPC instead. I've recently started rolling it out in my own services, and it's unexpectedly great considering the track-record of similar ideas. It's very performant, pleasant to work with, has a mature ecosystem of surrounding tools, and you get client API implementations in a wide range of languages for "free" (or at least at a cut price).

[cainlevy]

My intention for the user-facing endpoints is that the host app will never need to see or accidentally log a user's password. It's a pattern inspired by credit card vaults.

Could you still achieve your deployment goals with a Gateway/WAF setup that proxies the user-facing endpoints? The only issue I'm presently aware of with this setup is https://github.com/keratin/authn-server/issues/8.

[cortesi]

Sure - in my case this would be a load balancer on Google Cloud configured through a Kubernetes ingress. All the public paths available on the Auth microservice would have to be listed explicitly. You have to be very sure in this scenario that only the public URLs are reachable.

I see the motivation for sending user passwords straight to AuthN, but I do wonder if on balance the dangers of correctly configuring a shared public/private service don't outweigh the dangers of relaying the password through your front-end (which has to be able to access private endpoints on the AuthN service anyway). If you really didn't want your front-end to touch passwords, you could have a tiny sidecar service that only exposes the public endpoints and speaks GRPC to AuthN.

Anyway, this is well into debatable "matter of opinion" territory, and I don't want to waste your time. Thanks for publishing AuthN - I'll keep a close watch as you progress.