Adds support for the Forward OAuth Identity feature in backend data source plugins.
Earlier this feature has only been supported for non-backend data source plugins.
Fixes#26023
Co-authored-by: Arve Knudsen <arve.knudsen@gmail.com>
Co-authored-by: Marcus Efraimsson <marcus.efraimsson@gmail.com>
OAuth token refresh fails when custom SSL settings are configured for
oauth provider. These changes makes sure that custom SSL settings
are applied for HTTP client before refreshing token.
Fixes#27514