RFC 234: support 5 WebTransport h3 servers with different certs

rfcs/webtransport_h3_multiple_certs_test_servers.md

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+# RFC 234: WebTransport over HTTP/3 Test Server support 5 instances with different certs for validation of certificate hash values
+
+## Summary
+
+Optionally start 5 instances of the [WebTransport over
+HTTP/3](https://datatracker.ietf.org/doc/html/draft-ietf-webtrans-http3-01)
+server in [RFC
+85](https://github.com/web-platform-tests/rfcs/blob/master/rfcs/webtransport_h3_test_server.md)
+in wpt, that uses instead of the standard certificate a set of self-signed
+certificates with different expiration statuses. The certificates are
+autogenerated at the startup of the wpt tests within the python code.
+
+## Details
+
+### Implementation
+
+It is a slight modification of the server from [RFC
+85](https://github.com/web-platform-tests/rfcs/blob/master/rfcs/webtransport_h3_test_server.md)
+in the `tools/webtransport` directory.  The implementation uses the
+`cryptography` lib for certificate generation, that is already used by wpt
+through the `aioquic` lib.
+
+This is needed to properly test the various requirements for certificate
+acceptance in the WebTransport spec: https://w3c.github.io/webtransport/#web-transport-configuration
+
+Proposed implementation is here:
+https://phabricator.services.mozilla.com/D278886
+and tests using it are here:
+https://phabricator.services.mozilla.com/D277256
+
+### Handlers
+See [RFC
+85](https://github.com/web-platform-tests/rfcs/blob/master/rfcs/webtransport_h3_test_server.md)
+for details.
+
+### `wptserve` integration
+
+See [RFC 85](https://github.com/web-platform-tests/rfcs/blob/master/rfcs/webtransport_h3_test_server.md) for details.
+
+This adds a python file to generate server certificates
+`tools/webtransport/cert_generator.py` and
+`tools/webtransport/generate_test_certs.py`. The tests can access the
+server certificate hashes via `tests/webtransport/handlers/cert-hash.py`.
+
+There is a 1-line modification to `environment.py` to define the additional
+ports use and a small change to `serve.py` to support starting multiple h3
+instances.
+
+### Dependencies
+
+The only dependency are `aioquic` as in RFC 85 and `cryptography`, which is already a dependency of `aioquic`.
+
+## Risks
+
+Risks are similar to [RFC
+#85](https://github.com/web-platform-tests/rfcs/blob/master/rfcs/webtransport_h3_test_server.md#risks),
+as it is a minimal modification of RFC 85, so that maintenance cost
+increase is neglible.