I see [AuthManager.java](https://github.com/solid/conformance-test-harness/blob/50cbd72739d00c176211bfa6184ef3c12b70a0d0/src/main/java/org/solid/testharness/http/AuthManager.java#L217-L218) will do a POST with fields [`"username"`](https://github.com/solid/conformance-test-harness/blob/59e9b16788e42231985793d1c7556e8717f99f57/src/main/java/org/solid/testharness/http/HttpConstants.java#L27) and [`"password"`](https://github.com/solid/conformance-test-harness/blob/59e9b16788e42231985793d1c7556e8717f99f57/src/main/java/org/solid/testharness/http/HttpConstants.java#L29). This works [for NSS](https://github.com/solid/web-access-control-tests/blob/main/run-against-nss.sh#L22) and [should also work for PSS](https://github.com/pdsinterop/test-suites/blob/main/servers/php-solid-server/cookie/app/index.js#L11-L12). For solid-nextcloud it will be harder because there we need Puppeteer to log in.