Bug: WebID profile discovery fails when server returns HTML instead of Turtle

[melvincarvalho]

Bug description:

When fetching a WebID profile for OIDC issuer discovery, the rdflib fetcher doesn't send an Accept header preferring RDF formats. If the server returns HTML (with embedded JSON-LD) instead of Turtle, the solid:oidcIssuer is not discovered and authentication fails.

Steps to reproduce:

1. Have a WebID profile that returns HTML by default (with JSON-LD) but Turtle when requested
2. Ensure solid:oidcIssuer is set in the Turtle representation
3. Try to authenticate to NSS using a token from that IdP
4. Authentication fails with "OIDC issuer not advertised"

Cause:

In preferred-provider.js, fetcher.load(webId, { force: true }) doesn't specify an Accept header. The server returns HTML, and rdflib fails to resolve relative URIs like @id: "#me" in the embedded JSON-LD.

Suggested fix:

const options = {
  force: true,
  headers: { 'Accept': 'text/turtle, application/ld+json, text/n3, application/rdf+xml' }
}
return fetcher.load(webId, options)

[ewingson]

deployed to NSS on solidweb.org:

~/.nvm/versions/node/v22.11.0/lib/node_modules/solid-server/node_modules/@solid/oidc-auth-manager/src/preferred-provider.js Line # 17