envoy: add a filter to store client cert info #4372
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Add a new Lua filter that will store client certificate info as dynamic metadata. This will allow us to configure client certificate validation at the Envoy listener level, and then pass the results of that validation into our ExtAuthz service. This also allows us to pass the entire client certificate chain (and not just the leaf certificate, which is how the 'include_peer_certificate' ExtAuthz setting behaves). This will allow us to add support for intermediate CA certificates supplied by the client. However, if a client certificate does not validate successfully by Envoy, we will not store the certificate chain. (This should help guard against any possibility of making policy decisions based on unvalidated client certificate data.)
kenjenkins
commented
Jul 19, 2023
| function envoy_on_request(request_handle) | ||
| local metadata = request_handle:streamInfo():dynamicMetadata() | ||
| local ssl = request_handle:streamInfo():downstreamSslConnection() | ||
| metadata:set("com.pomerium.client-certificate-info", "presented", |
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Let me know if you have any opinions on the metadata namespace to use for this data. The only guidance I've found from the Envoy documentation is this:
Key is the reverse DNS filter name, e.g. com.acme.widget. The envoy.* namespace is reserved for Envoy’s built-in filters.
However, this metadata is for consumption by our ExtAuthz service, which can apparently ask for any metadata namespaces it likes, so I don't think this needs to correspond exactly to a filter name.
Again, happy to change this if you have an opinion about what it should be.
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Summary
Add a new Lua filter that will store client certificate info as dynamic metadata. This will allow us to configure client certificate validation at the Envoy listener level, and then pass the results of that validation into our ExtAuthz service.
This also allows us to pass the entire client certificate chain (and not just the leaf certificate, which is how the 'include_peer_certificate' ExtAuthz setting behaves). This will allow us to add support for intermediate CA certificates supplied by the client.
However, if a client certificate does not validate successfully by Envoy, we will not store the certificate chain. (This should help guard against any possibility of making policy decisions based on unvalidated client certificate data.)
Related issues
#4352
User Explanation
Checklist
updated docs[n/a]updated unit tests[n/a]updated UPGRADING.md[n/a]improvement/bug/ etc)