Self-Signed JWTs
65 comments
·August 1, 2025maxwellg
tempest_
Back in the day I worked at a place that had HMAC signing on an http endpoint.
50% of the support issues were because people could not properly sign requests and it caused me to learn how to make http in all sorts of crap to help support them.
danscan
Easy to imagine that haha. That’s part of the reason I’d lean on a standard like JOSE and make signing happen automatically for users who prefer to use an SDK
crabmusket
> sign a JWT per request
That's interesting - why do it this way rather than including a "reusable" signed JWT with the request, like an API token? Why sign the whole request? What does that give you?
Also what made that API so nice? Was this a significant part of it?
motorest
> That's interesting - why do it this way rather than including a "reusable" signed JWT with the request, like an API token? Why sign the whole request?
Supposedly bearer tokens should be ephemeral, which means either short-lived (say single-digit minutes) or one-time use.
This was supposed to be the way bearer tokens were supposed to be used.
> What does that give you?
Security.
dwaite
> Supposedly bearer tokens should be ephemeral, which means either short-lived (say single-digit minutes) or one-time use.
The desirable properties for tokens is that they have some means of verifying their integrity, that they are being sent by the authorized party, and that they are being consumed by the authorized recipient.
A "reusable" bearer JWT with a particular audience satisfies all three - as long as the channel and the software are properly protected from inspection/exfiltration. Native clients are often considered properly protected (even when they open themselves up to supply chain attacks by throwing unaudited third party libraries in); browser clients are a little less trustworthy due to web extensions and poor adoption of technologies like CSP.
A proof of possession JWT (or auxiliary mechanisms like DPoP) will also satisfy all three properties - as long as your client won't let its private key be exfiltrated.
It is when you can't have all three properties that you start looking at other risk mitigations, such as making a credential one time use (e.g. first-use-wins) when you can't trust it won't be known to attackers once sent, or limiting validity times under the assumption that the process of getting a new token is more secure.
Generally an extremely short lifetime is part of one-time-use/first-use-wins, because that policy requires the target resource to be stateful. Persisting every token ever received would be costly and have a latency impact. Policy compliance is an issue as well - it is far easier to just allow those tokens to be used multiple times, and non-compliance will only be discovered through negative testing. Five minutes is a common value here, and some software will reject a lifetime of over an hour because of the cost of enforcing the single use policy.
I haven't seen recommendations for single-digit minute times for re-issuance of a multi-use bearer token though (such as for ongoing API access). Once you consider going below 10 minutes of validity there, you really want to reevaluate whatever your infrastructure requirements were that previously ruled out proof-of-possession (or whether your perceived level of risk-adversity is accurately represented in your budget)
maxwellg
Each JWT was passed as a query param over a 307 redirect from my service to the other side, so the JWT itself was the whole request to prevent tampering from the browser. It was for an internal tool that did one thing, did it well, and never caused me any problems.
lll-o-lll
> Unfortunately they represent a huge usability hit over API Keys for the average joe. Involving cryptography to sign a JWT per request makes an API significantly harder to consume with tools like Postman or CURL.
Just generate the JWT using, e.g. https://github.com/mike-engel/jwt-cli ? It’s different, and a little harder the first time, but not any kind of ongoing burden.
You can even get Postman to generate them for you: https://learning.postman.com/docs/sending-requests/authoriza..., although I have not bothered with this personally.
maxwellg
Installing a dependency for myself is just and a little harder the first time. Asking every developer who will ever consume my service over CURL to install a dependency is absolutely an ongoing burden.
danscan
IMO this is a tooling issue. You can make your SDK generate keys and even base64 encode them so they appear opaque to the uninitiated (like an API key)
actinium226
Interesting, so instead of OpenAI giving me an API key, I give them a public key, which they register. Sounds like what we already do with GitHub. I like it.
deathanatos
Which, unless I'm missing something, undercuts the entire article? The private key, in the generated keypair, is the thing that you can then never commit to your VCS.
When you "register" the public key with whatever the relying party is, you're also likely going to bind it to some form of identity, so you can't leak this private key to others, either. (And I'm curious, of course, how the relying party comes to trust the public key. That call would seem to require its own form of auth, though we can punt that same as it would be punted for an API key you might download.)
kennywinker
Sorry, are you expecting some way to authenticate without any secrets?
Could you describe how that would work? If two people have the same info, how on earth do you tell which is which?
The post is talking about simplifying things by eliminating all the back and forth. It’s not pretending to invent a secret-less auth system.
deathanatos
> Sorry, are you expecting some way to authenticate without any secrets?
I'm not. "It’s truly wild to me what some of y’all will tolerate." What, exactly, are we tolerating that is solved by asymmetric key pairs?
> The post is talking about simplifying things by eliminating all the back and forth. It’s not pretending to invent a secret-less auth system.
Well, then, I'm lost. What back & forth was eliminated?
In one system, we download an API key. In this system, we upload a public key. In both, we have a transfer; the direction doesn't really matter. Someone has to generate some secret somewhere, and bind it to the identity, which is what I was saying above, and is apparently the wildness that I'm tolerating.
hinkley
In theory, I as the service provider know when my key database has been compromised. In theory. In practice, I will never know if a customer has been compromised, however up to a point a compromised user box can forward tokens to an attacker. So pending on whether you ever rotat the private keys, it’s a matter of ho long an attacker can retreat to a server they own to continue the attack.
In a way this reminds me a bit of SRP, which was an attempt to handle login without the server ever having your password. Which makes me think this is something to be integrated with password managers.
PantaloonFlames
Yes.
and it’s easy to do keypair generation in the browser using subtle crypto. That API doesn’t provide jwk generation, but seems like it would be relatively easy to do even without the jose module. And the browser cab “download” (really just save) the keypair using the Blob API. Keys need not leave the browser.
An api developer portal could just offer - generate a new keypair? - upload your existing public key?
…As a choice. Either way the public key gets registered for your account.
The end. Easy.
johncolanduoni
This is actually how GCP has always done service account authentication. A GCP service account key is an asymmetric keypair and Google stores the public key. AWS is somewhat similar, but they use an symmetric HMAC so they store the same secret key you use.
danscan
It's interesting to imagine taking the pubkey as identity concept to its full extents in situations like this, for example if you could create a cloud account, spin up resources, and authorize payment for them all programmatically without having to enter payment details on a form (because your keypair can authorize payment with the whatever payment method you use)
lokar
Even better if they would take a private CA cert.
esseph
This is similar to ssh key auth. (Pubkey, privkey)
827a
Even better: Imagine a world where you could just host your public keys on e.g. mydomain.com/.well-known/jwks.json, you register with a service provider with me@mydomain.com, then the service automatically pulls public keys from that. Then, all you have to do is sign new keys with an appropriate audience like aud:"serviceprovider.com".
And for the public email providers, a service like Gravatar could exist to host them for you.
Wouldn't that be nice.
beckthompson
Github has a cool little article on making JWTs for their API. Very useful!
https://docs.github.com/en/apps/creating-github-apps/authent...
The JWT website is also super useful https://www.jwt.io/
woodruffw
I feel like I’m not understanding the target audience for this post: are there people/companies out there specifically paying other companies to be their key-holding party for JWT issuance purposes? I know about SSO providers of course, but that’s several layers of abstraction up.
(Maybe my confusion here is that these JWTs are being described as self-signed, as if there’s a JWK PKI cabal out there, like the bad old days of the Web PKI. There isn’t one that I know of!)
danscan
The key distinction I am getting at is: self-signed as in “signed with a self-issued key pair”, as opposed to using an API key/credential that has been issued to you
jauntywundrkind
The model here feels not entirely dissimilar to Passkeys? Both are user provided auth tokens??
[Ed: allegations that the following is inaccurate! Probably checks out? Yes I meant the browser not the domain bound part, that seems solid.] Pity that Passkeys are so constrained in practice by browsers, that using them pretty much requires you trust the cloud providers absolutely with all your critical keys.
johncolanduoni
They're not constrained that way at all. The communication between browsers and various passkey-holding software and hardware is an open standard. There are open-source apps that can hold and sync passkeys. I don't know why everyone keeps repeating this obvious falsehood.
danscan
Not sure which way of constraint you're referring to, but WebAuthn credentials are bound to a domain via Relying Party ID.
There's a proposal for cross-domain usage via Related Origins, but that scheme depends on the authority of the relying party, meaning you can't say "I'd like to be represented by the same keypair across this set of unrelated domains"
johncolanduoni
I was referring to this:
> Pity that Passkeys are so constrained in practice by browsers, that using them pretty much requires you trust the cloud providers absolutely with all your critical keys.
Passkeys are not constrained so you have to trust cloud providers or anyone else with all your critical keys. The key is resident in whatever software or hardware you want to use, and anyone can create passkey software or hardware that will work with Chrome etc. I'm talking about (and I'm pretty sure the OP was referring to) the other side of WebAuthn: where the credentials surfaced to JavaScript via WebAuthn actually come from and how the browser relays requests that a challenge is signed.
danscan
Yeah, I am sort of a fan of Passkeys in principal, but they are domain bound (you can't use them across domains).
I wish there were something built into browsers that offered a scheme where your pubkey = your identity, but in short there are a lot of issues with that
jacobljohnston
This is already something in mainstream authentication applications you host yourself on your own domain. We use Keycloak. I don't know why anyone would install a JavaScript library to do this. It's not that difficult.
vips7L
I wish someone would have used keycloak at my place. They decided to write it all by hand instead.
danscan
Fair. I assume you mean asymmetric key cryptography and not JWKs in particular? JOSE is a pretty good library if you need the latter and you’re already working in JS
motorest
> Fair. I assume you mean asymmetric key cryptography and not JWKs in particular?
There's some degree of confusion in your comment. JWKs is a standard to represent cryptographic keys. It is an acronym for JSON Web key set.
> JOSE is a pretty good library (...)
JOSE is a set of standards that form a framework to securely transfer claims.
jacobljohnston
We’re using JWKs.
danscan
Ah, and just the subtle crypto API to generate keys? Or are you not generating them on the client?
distalx
On the B2B2C section, my mind immediately went to OAuth. For a developer like Bob giving his end users access to a service, wouldn't a standard OAuth flow where his users grant permission to his app would be the more conventional and secure solution?
It feels like that model handles key management, delegation, and revocation in a well-established way.
What am I missing here that makes this a better fit?
motorest
> What am I missing here that makes this a better fit?
From a cursory read, the answer is "it doesn't".
The blogger puts up a strawman argument to complain about secret management and downloading SDKs, but the blogger ends up presenting as a tradeoff the need to manage public and private keys, key generation at the client side, and not to mention services having to ad-hoc secret verification at each request.
This is already a very poor tradeoff, but to this we need to factor in the fact that this is a highly non-standard, ad-hoc auth mechanism.
I recall that OAuth1 had a token generation flow that was similar in the way clients could generate requests on the fly with nonces and client keys. It sucked.
JohnMakin
is the author suggesting allowing the client to set their own claims and using that to auth whatever action they are going to take? I have to be misunderstanding what they are saying - that sounds fraught with risk
danscan
(Author here) The JWT signer should be the authority setting claims, so if your server is the authority and the client is untrusted, the server can provide the client a pre-signed JWT with the claims it needs, and the client can send that along with requests to the API.
But this scheme is flexible. You could also have the client send "requested" claims for the server to consider adding if allowed when getting a JWT.
You could also reverse-proxy client requests through your server, adding any claims the server allows.
danscan
In some apps, the client may be the signing authority (e.g. it owns the resource it's accessing).
In that case, the client can possess the JWK keypair and do its own signing.
reactordev
Some engineers forgot the secret/salt part of generating the jwt. Sometimes you can just pack some claims in there and encode it and it works!!
marifjeren
> Visit our website. Create an account. Verify your email. Create a project. Add your credit card. Go to settings. Create an API key. Add it to your password manager. Drop it in your .env file. Download our SDK. Import it. Pass your env var in. Never share your API key. Make sure you never commit it to source control.
None of this "BS" actually goes away with self-signed JWTs, right? Just replace mentions of "API Key" with public/private key and it's otherwise a similar process I think.
danscan
The things that change are:
1. With self-signed JWTs, you could start consuming APIs with free tiers immediately, without first visiting a site and signing up. (I could see this pattern getting traction as it helps remove friction, especially if you want to be able to ask an LLM to use some API).
2. Compare this scheme to something like the Firebase SDK, where there's a separate server-side "admin" sdk. With self-signed JWTs, you just move privileged op invocations to claims – consuming the API is identical whether from the client or server.
3. The authority model is flexible. As long as the logical owner of the resource being accessed is the one signing JWTs, you're good. A database service I'm working on embeds playgrounds into the docs site that use client-generated JWKs to access client-owned DB instances.
kassner
> you could start consuming APIs with free tiers immediately, without first visiting a site and signing up
I’m yet to see a website that provides an API and doesn’t have a ToS that you have to agree to. Unless you control both parties, or you expose your service only to pre-vetted customers, there is no legal department that is going to allow this.
simsla
The problem I see with (1) is that it becomes a little bit too easy to regenerate public keys and circumvent free tier metering.
actinium226
I guess that's easily addressed by requiring an account and a public key to access the free tier. Still better than having to get yet another API key.
danscan
For sure. Would likely need to be combined with another mechanism like IP rate limits
null
tonyhart7
what is this drawback???? surely there must be a catch somewhere right??? if its that easy then everyone would love to use this
rvz
This article uses "ES256" for the alg, GitHub uses "RS256" as their alg and a very deranged few use "none".
The point here is this article is giving the developer lots of rope to hang themselves with the JOSE standard on JWT/K/S and it is a sure way to implement it incorrectly and have lots of security issues.
PASETO is a much better alternative to work with: https://paseto.io with none of the downsides of the JOSE standard.
jillesvangurp
Yes you can create unsigned JWTs. Don't do that and don't accept any such tokens as valid (which would be the even bigger facepalm worthy mistake).
Just do it right (and at this point it is widely documented what the pitfalls are here), comply with the widely used and commonly supported standards, and follow the principle of the least amount of surprise. Which is kind of important in a world where things need to be cross integrated with each other and where JWTs, JOSE, and associated standards like OpenID connect are basically used by world+dog in a way that is perfectly secure and 100% free of these issues.
Honestly, it's not that hard.
The paradox with Paseto is that if you are smart enough to know what problem it fixes, you shouldn't be having that problem and also be smart enough to know that using "none" as an algorithm is a spectacularly bad idea. You shouldn't need Paseto to fix it if you somehow did anyway. And of course you shouldn't be dealing with the security layer in your product at all if that is at all confusing to you.
danscan
Haven't heard of PASETO, but I'll check it out. I'd say JOSE is an implementation detail of what I'm advocating for, so very open to alternatives.
JimDabell
JWTs and JOSE have a bad reputation for footguns and ignoring modern cryptographic principles.
PASETO is the “mostly fixed” version of JWTs, but if you’re looking for something with more features, biscuits are quite interesting:
nabwodahs
That site is blocked by Fortinet as "pornography."
garganzol
Modern day AV software:
isCornography = url.contains("corno") || url.contains("body") || url.contains("self");
isVirus = url.contains("virus") || competitorUrlRegex.matches(url);snickerdoodle12
Did you contact Fortinet since you're the one that apparently utilizes them?
I _love_ JWTs for API authentication - one of the nicest APIs I ever consumed was essentially JSON RPC over JWTs. Unfortunately they represent a huge usability hit over API Keys for the average joe. Involving cryptography to sign a JWT per request makes an API significantly harder to consume with tools like Postman or CURL. You can no longer have nice click-to-copy snippets in your public docs. You either have an SDK ready to go in your customer's language or ecosystem of choice, or you're asking them to write a bunch of scary security-adjacent code just to get to their first successful request. No, I don't have a JWT library recommendation for Erlang, sorry.
Not that an API couldn't support both API Keys and JWT based authentication, but one is a very established and well understood pattern and one is not. Lowest common denominator API designs are hard to shake.