Added dropdown to select whether to send credentials in header or body in client credentials flow

Editor assessment

The subject describes the addition concretely — a dropdown selects whether credentials are sent in header or body for the client credentials flow — though it runs long and the past-tense phrasing is loose. The body's squash bullets add test context but end with 'Oopsie', a throwaway note that signals process noise. The fix type is arguable for what is a feature; the rubric tolerates straddling choices. No malformed footers appear. Understandable, but the length, informality, and thin rationale hold it at acceptable.