We don't want every Service Provider to be able to request
every endpoint if those are not implementing a filtering on
the data returned. To prevent any data leak we enforce the
developers to manually "whitelist" each endpoint and add
the proper filtering when needed.
Tests are missing, let's ship it, I'll open an issue.
Without such protection, the whole app would crash if the resource server is
not configured. The fallback backend would return an appropriate error to
the client if the resource server is improperly configured.
Overload mozilla-django-oidc class to support an authentication method
with the resource server backend.
This enables any route of the API to be called with an access token
issued by Agent Connect.
Why:
Many services in La Suite rely on Agent Connect to authenticate their users.
Delegating authentication to Agent Connect is highly beneficial. With a central
party (Agent Connect) handling user authentication, our services can seamlessly
communicate with each other. Our backend must be able to receive and verify
access tokens issued by Agent Connect.
Additionally, it should ensure that the resource owner has granted permission
for our data to the service provider transmitting the access token.
How:
Our backend needs to verify access tokens by introspecting them. This involves
requesting the Authorization Server to validate the access token received in
the authentication header. The Authorization Server validates the token's
integrity, provides authentication and authorization information about
the user currently logged into the service provider requesting data from
the resource server.
The data returned by the Authorization Server to the resource server
is encrypted and signed. To encrypt the introspection token, the Authorization
Server retrieves the resource server's public key from
the new ‘/jwks’ endpoint.
Encryption parameters, such as algorithm and encoding, are configured on
the resource server. Ensure that these parameters match between
the Authorization Server and the resource server.
The resource server verifies the token signature using the Authorization
Server's public key, exposed through its `/jwks` endpoint. Make sure
the signature algorithms match between both servers. Finally, introspection
token claims are verified to adhere to good practices for handling JWTs,
including checks on issuer, audience, and expiration time.
The introspection token contains a subject (`sub`). The resource server uses
this subject to retrieve the requested database user, compatible
with both pairwise and public subjects.
Important:
Agent Connect does not follow RFC 7662 but uses a draft RFC that adds security
(signing/encryption) to the initial specification. Refer to the "References"
section for more information.
References:
The initial RFC describing token introspection is RFC 7662 "OAuth 2.0 Token
Introspection". However, this RFC specifies that the introspection
response is a plain JSON object.
In eGovernment applications, our resource server requires stronger assurance
that the Authorization Server issued the token introspection response.
France Connect's team implemented a stronger version of the spec, returning
a signed and encrypted token introspection response. This version is still
a draft, available under:
"draft-ietf-oauth-jwt-introspection-response".
In OAuth 2.0, the Authorization Server is equivalent to the OIDC provider.
The Authorization Server exposes endpoints for token introspection and JWKS.
I’ve created a client to easily interact with the Authorization Server,
while doing the token introspection in our resource server.
Token introspection will be explained in upcoming commits.
The current OIDC library used in the project doesn’t offer token introspection,
leading to redundancy in the code handling some OIDC/OAuth2 flows.
This overlap makes the code bulky. My goal is to quickly deliver a working
PoC for the resource server, with plans to refactor in the longer run.
Please feel free to provide feedback on the class design.
Introduce a new endpoint, /jwks, which returns a JSON Web Key Set (JWKS).
This set of public crypto keys will be used by external parties to encrypt
data intended for our backend. In the context of the resource server, this key
will be used by the authorization server to encrypt the introspection response.
The current implementation exposes a single public key, with the private key
configurable in the app settings. The private key is represented as a string.
For enhanced security, we might prefer to store this data in a .pem file
excluded from version control.
A few parameters for this key, such as its type and encoding, are configurable
in the settings.
A critique of the current design is its lack of extensibility.
If we decide to offer more than one encryption method, this view will require
refactoring.
Additionally, the current implementation is tightly coupled with joserfc.
This lays the foundation for further improvements.
Please note, this endpoint only public components of the key, there is no
chance for any secret leaking.
