most of my knowledge about oauth is about using it at my dayjob for years, so don't take my answer with any authority. its more a users perspective of the technology then how it was actually meant to be used, which i do not know.

first off: the whole idea of using oauth in your systems is to externalize authentication. its main usecase is if you have several services which share the same users... usually microservices, but everything else which supports oauth works as well, obviously

if you do not actually want to externalize your authentication, then oauth is likely not what you actually want. (keep in mind this only applies to the process of authentication. you will probably still create a `users` table to put a foreign key on your domain entities. said users table just won't have a `password` field or similar)

under this perspective it makes sense that you basically only find blog posts to integrate 3rd party tools, right? you're just setting out to implement a new oauth2 server otherwise after all, and... i'd strongly suggest you don't. there are so many pitfalls you can fall into. its not a trivial subject.

thankfully, there are readily available FOSS oauth2 servers like keycloak around if thats what you want to use...

but to come back to my initial point: if you do not want to externalize your authentication, then do not use oauth! almost all frameworks already have tools available you can use to authenticate with api tokens. it keeps you within the bounds of your frameworks strength and you can automatically fetch a token on your frontend after the user authenticated with your usual flow.

but i'm already off topic considering your first question. if you do use a solution like keycloak, there are `oauth clients`. these behave exactly as you want.

> first off: the whole idea of using oauth in your systems is to externalize authentication. its main usecase is if you have several services which share the same users... usually microservices, but everything else which supports oauth works as well, obviously

We don't want to externalize it. For clarity _(because i think i implied internal API->API)_, our primary concern right now is a client API interfacing with our API. We want to choose some implementation that clients would expect, and easily reason about.

There may be a future where those clients have to authenticate to multiple APIs / microservices of ours, but currently it is one API setup for this explicit purpose.

> but to come back to my initial point: if you do not want to externalize your authentication, then do not use oauth! almost all frameworks already have tools available you can use to authenticate with api tokens.

Yea, not using Oauth was my thought was well. My concern however, was trying to pick something clients would expect. I don't want it to feel custom, arbitrary, hodgepodge.

Our very early impression / plan is to use a token renewal, and a shortlived token, similar to oauth. However this loose, and custom, and i don't want clients feeling like we're making things up. Hell, i don't want to make things up.

My current thought is that I need to research JWT more, as it may fit what we need, and be more standardized.

edit: And PASETO

You should probably just try out a foss oauth server to get a feel for it.

Just start a keycloak server with docker and write a small Webservice in your language of choice which only let authenticated users open the website, which just prints the user name for example.

After you did that, you could write a second service which accesses that api using a client (not user) and prints which users have accessed it since it was started.

That should be doable within a few hours at most and give you a feel for the technology.

If you're fluent in python, I'd personally suggest just starting a hello world flask project, connect it to a keycloak and write a second cli script which simulates the non-user access. (If you use Java, keep in mind that springboot2 uses Springsecurity5, which was incompatible with the official keycloak Java sdk the last time I checked. Either use springboot1 or expect to have a slightly harder time figuring out what to write in the application.properties)

Reimplementing advanced authentication systems like jwt on your own is extremely error prone and frankly unnecessary if you're not in the business of authenticating users. I'd suggest to either use whatever your framework prefers (which is usually just a static and very long, manually rotated token) or try to externalize it by using readily available foss solutions

> Yea, not using Oauth was my thought was well. My concern however, was trying to pick something clients would expect. I don't want it to feel custom, arbitrary, hodgepodge.

I think clients often expect one of the following (assuming everything is done over HTTPS): 1. HTTP basic auth 2. Login to the API, get a token, and use that token for requests 3. Generate an API key for the client and the client sends the key on every request 4. (Occasionally) Cryptographic signing of every request, sending the signature with the request

1 and 3 (if implemented as a username/password on the back end) are going to have similar trade offs. You are fully authenticating every request that comes in against your credentials data store.

Option 2 is where OIDC/OAuth2 comes into play or you could use a standard session token approach if you want. In OAuth terminology the client credentials grant is the simple flow where the client logs in with a username/password, gets a token back, and includes that token in API calls. Option 2 is also valuable if you want to support mobile clients with refresh tokens and such using things like the authorization code grant. Essentially allowing users to login to a mobile app once but use short-lived tokens when calling the API without prompting users for credentials every few minutes.

Option 4 can be an alternative to token-based approaches to reduce load on your credentials database but gets more complicated for the client.

Ultimately if you are looking to keep things simple I would lean towards HTTP Basic auth until/unless you are building a mobile app or otherwise really need to move to a token-oriented approach. At that point I would consider full fledged OIDC/OAuth2 or maybe a login that generates an API session token.

I've been doing a similar thing recently. I found PASETO to be interesting ( https://paseto.io ), which is a lot like JWT but is simpler and more opinionated (e.g. there is no plaintext option; symmetric and asymmetric operations are cleanly separated; etc.). I especially enjoyed watching this video https://youtu.be/RijGNytjbOI

I still decided to go with JWT, since PASETO isn't yet standard and its software hasn't been around for long, but it definitely helped me understand more about the choice I was making. In particular, PASETO distinguishes between "local" tokens (producer and consumer can both use the same symmetric key) versus "public" tokens (producer and consumer can't use the same key, e.g. third party services run by different organisations; hence asymmetric keys are needed). PASETO encourages local tokens to be used when possible, since their keys can be shorter, they generate shorter tokens, they're faster to encrypt/decrypt, they're easier to rotate, etc.; public tokens are essentially a last resort when we must interact with a third party.

I was originally considering 'public' JWTs (i.e. asymmetric keys) for my use case, since we're using AWS API Gateway and that has the option to check the signatures of 'public' JWTs, and reject invalid ones before they ever hit my code. However, I eventually went with 'local' JWTs (i.e. symmetric keys), since the convenience of having AWS discard some tokens for us wasn't worth the (mostly logistical) overhead of using asymmetric keys.

My choice to use the JJWT library was also partly due to its recommendation by the JPaseto library ( https://github.com/paseto-toolkit/jpaseto ).

PASETO looks interesting, thank you!

Since my primary concern is external client APIs communicating with ours securely, but also in a way that's not too-foreign. I imagine JWT would fit the bill of being widely known, but PASETO sounds really interesting too - having less things to get wrong sounds amazing. My concern with PASETO is that client APIs are huge slow customers, so i'm hesitant to choose anything that's not super mainstream.

I'll research PASETO more, but i feel like my decision would come down to fitting to what the customer can use - less change is more, in that case. Ie, JWT.

Jwt works in this case... You issue a key to a known user.. In this case you create an API user (doesn't have to exist in a backing store) and set the expiration to a super short duration and validate it on the other end... You can also use this for API testing in unit/integration tests

OAuth is perfectly valid as a standard for inter-API authentication but it is complicated. You'll also have to figure out separately how your oAuth clients manage the secrets they use to authenticate to the oAuth server to retrieve access tokens, and if encryption as well as authentication between the APIs is important to you, how to manage the keys to do so.

Take a look at https://spiffe.io/ which avoids these concerns focuses specifically for system to system authentication at scale.

This is extremely context dependent. With just a few services, you can generate and statically place a few random strings to use as bearer tokens. In a more complex microservices environment, you want some way for the scheduler to participate in identity issuance, for example SPIFFE. Also consider whether the applications can actively participate in the scheme, or if it needs to be abstracted through sidecar proxies. Also consider whether you are doing TLS. Bearer tokens on plaintext connections are weak; maybe you need HMACs. Or to sort out TLS first. Then consider whether you need tokens at all, or can just use client certificates. Etc.

Where are you blocked in this use case?

The easiest flow IMO: The API client needs a service account (username and password like a human). It authenticates to the OIDC server with the username/password and obtains a token. Then it can call any API service with the token.

It's quite straightforward really.