MyUplink OAuth authorize returns invalid_request

[frahlg]

Bug Description

A Discord tester on v0.123.x reaches MyUplink's authorize page but MyUplink immediately renders:

Error
Sorry, there was an error: invalid_request
Request Id: 0HNM2R2L75RD7:000002B1

This happens before the redirect back to 42W, so it is likely an authorize URL parameter issue rather than the callback/token exchange path.

Evidence / suspicion

• Screenshot from Discord reporter Göran Andersson in #support, 2026-06-20.
• Current authorize URL builder sends scope as READSYSTEM offline_access.
• Earlier investigation noted MyUplink/Azure B2C may expect API scopes in fully-qualified form rather than bare READSYSTEM, and the portal does not expose manual scope selection.

Expected Behavior

Clicking Connect to MyUplink should show a MyUplink login/consent page and return an authorization code.

Actual Behavior

MyUplink displays invalid_request at api.myuplink.com immediately.

Environment

• Component: MyUplink OAuth setup / go/internal/api/api_myuplink_oauth.go
• Reporter: Discord Göran Andersson
• Related: MyUplink driver uses unsupported client_credentials OAuth flow #496 / MyUplink: authorization-code OAuth + in-app consent + heat-pump dashboard #497

Next steps

Capture the exact generated authorize URL minus secrets (client_id can be redacted) and test whether MyUplink requires fully-qualified scopes, different scope set, or rejects PKCE/redirect_uri for this app type.