Add an environment variable to allow forcing either the stateful or the
stateless authenticate flow.
Split the existing integration test clusters "single" and "multi" into
four new clusters: "single-stateful", "single-stateless",
"multi-stateful", and "multi-stateless", so that the integration tests
will run for both the stateful and the stateless authenticate flows.
(The "kubernetes" cluster is not currently being run, so I've left it
alone for now.)
* integration test config: add downstream mTLS routes
Add two new CA certificates for use with downstream mTLS tests, and a
client certificate/key pair issued by each CA.
Add a few routes to the policy template that require a client CA. Update
the generated output configurations.
(based on commit ed63a6a6e7)
* add downstream mTLS integration test cases
These are modeled after the tests added to v0.17 in 83957a9, but here
the expected behavior is that requests with an invalid client
certificate will receive a 495 response only after authentication.
