RFC9068 Access Token Validator

This library provides a means to validate access tokens following the rules laid out in RFC9068.

Rationale

Both OIDC and OAuth2 do not clearly specify how to validate access tokens as a resource server. This poses a risk as the implementation of choice might differ across applications and may be insecure.

In order to resolve this issue RFC7662 was published in 2015. This method involves the resource server sending the access token to the authorization server to verify it. This comes with a big performance penalty, as the resource server needs to make its own request to the authorization server everytime it needs to validate a token, which basically needs to happen for every authenticated request.

To overcome the performance penalty, systems started using access tokens in the form of JSON Web Tokens, which can be parsed and validated. However, considering there was no formal definition of what the contents of the token should look like, tokens issued by one provider were not necessarily compatible with tokens provided by another provider, leading to different implementations of token validation.

RFC9068 aims to overcome that obstacle by providing a specification on what the contents of the access tokens should look like and how to validate the access tokens.

Installation

Install using uv:

uv add rfc9068

or using pip:

pip install rfc9068

Usage

The validator itself is nothing more than a composition, its dependencies do the actual work. That means that we need to construct the validator and it's recommended to use dependency injection to do that, otherwise perhaps implement a factory.

Factory example

from rfc9068 import RFC9068AccessTokenValidator, RFC9068AccessTokenValidatorInterface
from rfc9068.parser import (
    AccessTokenParser,
    HeaderParser,
    Padder,
    PayloadParser,
    SignatureParser,
)
from rfc9068.payload import (
    IssuerValidator,
    AudienceValidator,
    ExpirationValidator
)
from rfc9068.signature import PyJwtSignatureValidator, PyJwtJWKResolver
from jwt import PyJWKClient, PyJWS

class ValidatorFactory:
    def __call__(
        self,
        jwks_url: str,
        issuer: str,
        audience: str,
        algorithms: list[str] = ["RS256"],
    ) -> RFC9068AccessTokenValidatorInterface:
        return RFC9068AccessTokenValidator(
            AccessTokenParser(
                Padder(),
                HeaderParser(),
                PayloadParser(),
                SignatureParser(),
            ),
            PyJwtSignatureValidator(
                PyJwtJWKResolver(
                    PyJWKClient(jwks_url),
                ),
                PyJWS(),
            ),
            IssuerValidator(),
            AudienceValidator(),
            ExpirationValidator(),
            algorithms,
            issuer,
            audience,
        )

factory = ValidatorFactory()
validate = factory(
  "http://keycloak:8002/realms/rfc9068/protocol/openid-connect/certs",
  "http://keycloak:8002/realms/rfc9068",
  "test-audience",
  ["RS256"],
)

Validator

Now that we have a validator we can use it to validate access tokens.

from rfc9068.core import InvalidTokenError

try:
  validate(access_token)
except InvalidTokenError as e:
  # Token is not valid
  print(e)
  raise e

# When no exceptions are raised the token is valid

Compatibility

The default implementation as seen above, works for access tokens that are strictly formatted using the format specified in RFC9068. However, unfortunately not all providers fully implement the specification (looking at you Microsoft). In order to be able to use this package with Entra ID for example we provide a special "compat" header parser. In this case we need that because Entra ID access tokens always have the value "JWT" in the typ header, whereas RFC9068 specifies that the value must be "at+jwt" or "application/at+jwt". This helps differentiate between different kinds of tokens, ID tokens would have the value "it+jwt" or "application/it+jwt", for example.

Because the risk of that is acceptable, we provide the following solution:

from jwt import PyJWKClient, PyJWS

from rfc9068 import RFC9068AccessTokenValidator
from rfc9068.compat import HeaderParser
from rfc9068.parser import (
    AccessTokenParser,
    InvalidHeaderError,
    Padder,
    ParsedAccessToken,
    PayloadParser,
    SignatureParser,
)
from rfc9068.payload import (
    AudienceValidator,
    ExpirationValidator,
    IssuerValidator,
)
from rfc9068.signature import (
    PyJwtJWKResolver,
    PyJwtSignatureValidator,
)


validate = RFC9068AccessTokenValidator(
        AccessTokenParser(
            Padder(),
            HeaderParser(),
            PayloadParser(),
            SignatureParser(),
        ),
        PyJwtSignatureValidator(
            PyJwtJWKResolver(
                PyJWKClient("http://keycloak:8002/realms/rfc9068/protocol/openid-connect/certs"),
            ),
            PyJWS(),
        ),
        IssuerValidator(),
        AudienceValidator(),
        ExpirationValidator(),
        ["RS256"],
        "http://keycloak:8002/realms/rfc9068",
        "test-audience",
    )

As you can see, this is almost the same as the factory example above, except the import of HeaderParser, which now comes from rfc9068.compat.

Development

For development of this package we provide a container setup.

Building

docker compose build

Starting containers

docker compose run --rm validator sh

This will also open a shell where we can run our dev tools:

uv run ruff check
uv run mypy .
uv run pytest -v --cov --cov-fail-under=100