Authenticator-rs has an optional feature webdriver which exposes a web service designed to implement the Virtual Authenticator API from WebAuthn.

The necessary work to hook it up and enable those Web Platform Tests is:

1. Make Gecko compile-in the webdriver feature
2. Make Gecko initialize the web service via the C interface when running in GeckoDriver mode. This will require a new C API point in authenticator-rs (https://github.com/mozilla/authenticator-rs/issues/144)
3. Add code to GeckoDriver (mozilla-central/testing/geckodriver/src) to proxy requests for /session/{session id}/webauthn to the authenticator-rs service, stripping off the /session/{session id} portion that GeckoDriver has to manage. (See https://github.com/mozilla/authenticator-rs/blob/main/webdriver-tools/webdriver-driver.py for example of what the authenticator-rs code expects)
4. Add code to GeckoDriver's capabilities model (https://searchfox.org/mozilla-central/source/testing/geckodriver/src/capabilities.rs) to reveal that WebAuthn is supported

Note that at step 3 we want to hook up marionette to authenticator_rs; that's where the actual implementation of WebDriver commands lives and will be enough to get the wpt working (since it uses marionette directly). GeckoDriver itself is more or less just a proxy between HTTP and marionette, so there are some changes required there but it's mostly just boilerplate.

I can provide any help required with the GeckoDriver and marionette parts.

The severity field is not set for this bug.
:jcj, could you have a look please?

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As this is work on geckodriver I'm going ahead and moving this bug to the appropriate component.

The bug assignee is inactive on Bugzilla, and this bug has priority 'P1'.
:whimboo, could you have a look please?

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Backed out for bustages on command.rs

Backout link: https://hg.mozilla.org/integration/autoland/rev/5954ce91542de618e7ccfc10bdfc5368b9160cb2
Log link: https://treeherder.mozilla.org/logviewer?job_id=425235238&repo=autoland&lineNumber=5933

Backed out for causing wpt failures in response.py

• Backout link
• Push with failures
• Failure Log
• Failure line: TEST-UNEXPECTED-FAIL | /webdriver/tests/classic/new_session/response.py | test_capability_type[webauthn:extension:credBlob-bool] - AssertionError: assert 'webauthn:extension:credBlob' in {'acceptInsecureCerts': False, 'browserName': 'firefox', 'browserVersion': '118.0a1', 'moz:accessibilityChecks': False, ...}

https://hg.mozilla.org/mozilla-central/rev/d918661c17e3

There is actually a problem with merging the upstream PR because the infrastructure test is failing:
https://github.com/web-platform-tests/wpt/pull/41377/checks?check_run_id=15772568550

Dana, can you please have a look?

(In reply to Henrik Skupin [:whimboo][⌚️UTC+2] from comment #16)

There is actually a problem with merging the upstream PR because the infrastructure test is failing:
https://github.com/web-platform-tests/wpt/pull/41377/checks?check_run_id=15772568550

Actually the following error might mean that we need a new marionette client release? James, is that correct? It at least doesn't fail in our CI which would explain that.

 0:15.65 CRITICAL Traceback (most recent call last):
  File "/home/test/web-platform-tests/tools/wptrunner/wptrunner/testrunner.py", line 158, in start_runner
    executor = executor_cls(logger, browser, **executor_kwargs)
  File "/home/test/web-platform-tests/tools/wptrunner/wptrunner/executors/executormarionette.py", line 1275, in __init__
    MarionetteRefTestExecutor.__init__(self,
  File "/home/test/web-platform-tests/tools/wptrunner/wptrunner/executors/executormarionette.py", line 1010, in __init__
    self.protocol = MarionetteProtocol(self, browser, capabilities,
  File "/home/test/web-platform-tests/tools/wptrunner/wptrunner/executors/executormarionette.py", line 745, in __init__
    do_delayed_imports()
  File "/home/test/web-platform-tests/tools/wptrunner/wptrunner/executors/executormarionette.py", line 55, in do_delayed_imports
    from marionette_driver.webauthn import WebAuthn
ModuleNotFoundError: No module named 'marionette_driver.webauthn'

Yes, that's correct.