I'm using OpenID Connect to control access to my REST API. One of the things I need to do when servicing a request is get the OIDC UserInfo based on the access token in request's Authorization: Bearer ... header.
To this point I've been working with JWTs and this works fine. I'm looking at expanding this to work with opaque tokens as well.
My strategy has been based on my understanding of the OpenID Connect Discovery spec, section 4:
Extract the iss from the access token.
Discover the userinfo endpoint by getting ${iss}/.well-known/openid-configuration and querying the JSON for userinfo_endpoint.
HTTP GET the userinfo_endpoint, passing the access token as an Authorization: Bearer ... header.
This works fine for opaque tokens... except for step 1. Currently, I have to know who the issuer is via an out-of-band mechanism because I don't know how to get the issuer from the opaque token (which, to be honest, makes sense given that it's opaque). I see a few possibilities:
Maybe I'm just supposed to know who issued it and my question is misguided.
Maybe the best thing to do is try a list of known issuers and see if one of them works.
Maybe there's a mechanism for discovering the issuer of the opaque token. (The spec refers to WebFinger, but that doesn't seem like it fits my use case.)
Maybe there's something I haven't considered...
Thanks all for any help.
The standard mechanism for dealing with opaque tokens is via introspection. Also the preferred option is for there to only be a single type of access token - issued by your Authorization Server (AS), which sits alongside your APIs.
The introspection result can be a claims payload or a JWT. It is common to plug in an API gateway, as in this article, so that the gateway makes the actual introspection call. The gateway should then cache results for subsequent calls made with the same access token.
An opaque token is typically a GUID or something similar, and the issuer value is not stored in the token - it is instead stored in the issuing Authorization Server's back end state. The only way to determine the issuer is to try to introspect the token.
FOREIGN ACCESS TOKENS
Aim to avoid using foreign access tokens in your APIs as in the following examples. This can make it difficult to control data added to tokens and token lifetimes:
User signs in with Google - then API uses Google access tokens
User signs in with Microsoft - then API uses Microsoft access tokens
It is preferred instead to use 'federated login capabilities' of your Authorization Server, leading to the following cleaner result, and fewer issues:
User signs in with Google - then API uses your AS access tokens
User signs in with Microsoft - then API uses your AS access tokens
Answering my own question:
You cannot discover anything from an opaque token alone.
An opaque token could be anything, even just a UUID that serves as a key to a database table in the Authorization Server. The only way anything can be obtained with such a token is by calling the introspection endpoint.
(Even if there is anything encoded in the opaque token, the only way it should be decoded is by calling the introspection endpoint.)
To that extent, my original question was somewhat misguided in that I was attempting to decode something that doesn't intrinsically express its encoding. It's rather like trying to use a pointer without knowing what it points to. Indeed, I've found a number of places where the term "reference token" is used to mean "opaque token."
Thanks to Gary Archer for some helpful feedback.
Related
While learning how OAuth2 works, I cannot figure out why there is a separate step to retrieve Access Token?
A separate step means:
an extract HTTP request
passing Client Secret in the URL
I'd expect the Access Token to be generated in the "authorization" step, encrypted with using the Client Secret, and returned back when redirecting to the Callback URL. Then the client application would decrypt it and use it straight await without issuing an extra HTTP request.
I guess there are some reasons behind having an extra step, and I'm just not aware of them. I hope you can explain the reasons in your answer.
I'm assuming you're talking about the Authorization Code flow and not the Implicit flow, which does return a token directly.
The Authorization Code flow is designed to work with potentially unencrypted servers via a callback URL (this was designed years before Let's Encrypt and the relatively recent encrypt-everything push). Thus, the URL could be intercepted by any intermediate routers/proxies, and sending an access code as part of the callback URL in that environment is a Bad Idea.
So instead, the authorization code is sent. Then the client exchanges the authorization code along with its client secret for an access token. The authorization code can be intercepted, but in the Authorization Code flow, the client secret is actually secret and not known outside your server, so any intercepted authorization code is useless on its own.
These days, encryption is common and free, and unencrypted flows are strongly discouraged. The extra call remains part of the Authorization Code flow for historical reasons.
Does an app using authorization code (with or without PKCE) to obtain access + id tokens on behalf of a user need to also validate those tokens (signature, not expired, audience, etc.)?
If so, what for? Since the client is using TLS and pointing to the provider it's been configured with, what attacks/threats does that client also validating the token mitigate?
At first glance you are right and the spec basically allows for not checking tokens directly returned from the token endpoint over TLS as you suggest indeed, but:
Firstly, one may argue that if a signature is present, it is there for a reason and it should be validated since the Provider is also free to return tokens without a signature (alg="none") if it did not want/need the Client to validate.
Secondly, there are known attacks ("IDP mixup") that trick the Client into talking to the wrong token endpoint as a way of stealing the Authorization Code: verifying that the ID token returned does not match the expected signature would at least stop the Client from processing an ID token produced by an attacker.
Thirdly, it would be good for the Client to protect itself against broken or compromised IDPs in general, avoiding replay attacks or similar.
I guess when you're doing all of it in a single domain, i.e. Client, AS and RS are all under control of the same organisation and the relationships between them are fixed and one-to-one only, technically verification would be overkill based on current knowledge and known attacks.
But in case your use case spans multiple security domain, in general it is better to verify than it is to assume.
I am not sure which approach I should be taking in our implementation and need some guidance.
I have a REST API (api.mysite.com) built in the Yii2 Framework (PHP) that accesses data from mysite.com (database). On mysite.com our users will be able to create Connected Apps that will provision a client id + secret - granting access to their account (full scope?).
Based on my research, the next step seems to be setting up something to actually provide the bearer tokens to be passed to the api - I have been leaning towards oAuth2, but then I read that oAuth2 does not provide authentication. Based on this I think I need OpenID Connect in order to also provide user tokens because my API needs to restrict data based on the user context.
In this approach, it is my understanding that I need to have an Authentication Server - so a few questions:
Is there software I can install to act as an OpenID Connect/oAuth2 authentication server?
Are there specific Amazon Web Services that will act as an OpenID Connect/oAuth2 Authentication Server?
I am assuming the flow will be: App makes a request to the auth server with client id + secret and receives an access token. Access token can be used to make API calls. Where are these tokens stored (I am assuming a database specific to the service/software I am using?)
When making API calls would I pass a bearer token AND a user token?
Any insight is greatly appreciated.
your understanding is not very far from reality.
Imagine you have two servers one for Authentication, this one is responsible for generating the tokens based on a Authorization Basic and base64 encoded CLientID / ClientSecret combo. This is application authentication basically. If you want to add user data as well, simply pass username / password in the post body, authenticate on the server side and then add some more data to the tokens, like the usernames, claims, roles, etc
You can control what you put in these tokens, if you use something like JWT ( Json Web Tokens ) then they are simply json bits of data.
then you have a Resource server, you hit it with a Authorization Bearer and the token you obtained from the Authorization one.
Initially the tokens are not stored anywhere, they are issued for a period of time you control. You can however do something else and store them in a db if you really want to. The expiration is much safer though, even if someone gets their hands on them they won't be available for long! In my case I used 30 minutes for token validity.
Now, you haven't specified what languages/frameworks you are looking into. If you use something like dot net then look into IdentityServer, version 4 is for Dot net core, 3 for anything below.
I also have a pretty long article on this subject if you are interested:
https://eidand.com/2015/03/28/authorization-system-with-owin-web-api-json-web-tokens/
Hopefully all this clarifies some of the questions you have.
-- Added to answer a question in comments.
The tokens contain all the information they need to be authenticated by the resource server correctly, you don't need to store them in a database for that. As I already said, you can store them but in my mind this makes them less secure. Don't forget you control what goes into a token so you can add usernames if that's what you need.
Imagine this scenario, you want to authenticate the application and the user in the same call to the Authorization Server. Do the OAuth2 in the standard way, which means authenticate the application first based on the client id / client secret. If that passes then next do the user authentication. Add the username or userid to the token you generate and any other bits of information you need. What this means that the resource server can safely assume that the username passed to it in the token has already been validated by the authentication server otherwise no token would have been generated in the the first place.
I prefer to keep these two separate myself, meaning let the AS ( Authorization Server) to deal with the application level security. Then on the RS (Resource Server) side you have an endpoint point like ValidateUser for example, which takes care of the user validation, after which you can do whatever you need. Pick whichever feels more appropriate for your project I'd say.
One final point, ALWAYS make sure all your api calls ( both AS and RS are just apis really ) are made over HTTPS and never ever have any important information transmitted via a GET call which means the URL can be intercepted. Both Headers and POST body are encrypted and secure over HTTPS.
This should address both your questions, I believe.
I need to add a token inside a token for an "act-as" schema on a custom grant type in IdentityServer3.
I tried with PreserveAccessToken but it just adds the token as a claim in the current ClaimsPrincipal, but can't find a way to nesting it as a claim when getting another token to pass along to the next service/api in the chain.
The idea behind this is for being able to keep an audit of all the hops from the end-user to the last service/api in a chain of calls.
This can be achieved using a custom grant. This allows extending the token endpoint with custom "operations" - e.g. issuing a token that contains delegated claims - e.g. a token.
docs are here: https://identityserver.github.io/Documentation/docsv2/advanced/customGrantTypes.html
here is also a sample that comes close to your scenario: https://github.com/IdentityServer/IdentityServer3.Samples/tree/master/source/Multi%20Hop%20Delegation%20(ActAsCustomGrant)
that said - this is probably the most expensive way to convey a user id over multiple hops.
If there is a trusted subsystem between the back-end system, simply transmitting the required data as payload is much simpler and much faster.
The big security issue always brought up when using OAuth2 seems to be centered around not technically being Authentication. However, if you are the owner of the identify provider and the resources being accessed, doesn't this accomplish authentication and thus make not necessary implementing a solution on like OpenID Connect on top?
In OAuth there's only one token that is being passed around (an access token) which is opaque to the Client/RP. The access token represents a capability that is given by an end user but it doesn't say anything about that user: not who the user is nor whether and how the user authenticated (because as said the token contains no information whatsoever by spec).
Anything that you can come up with would lead to an extension of OAuth 2.0 by adding the information described above in the (or a different) token - thus make it no longer opaque to the RP - and/or define an endpoint where that information about the user can be obtained. But then this extension would be exactly what OpenID Connect has standardized so it would not make much sense to deviate from that.