Verify the AssemblyAI webhook's shared-secret header. Throws
AssemblyAIWebhookAuthError on misconfiguration ("missing-secret")
or on a missing/wrong header ("invalid-secret"). The caller decides how to
surface these — typically 4xx for misconfig, 401 for invalid.
Verify the AssemblyAI webhook's shared-secret header. Throws AssemblyAIWebhookAuthError on misconfiguration ("missing-secret") or on a missing/wrong header ("invalid-secret"). The caller decides how to surface these — typically 4xx for misconfig, 401 for invalid.