Add fail-fast on init for missing provider credentials

internal/observability/metrics_middleware.go

@@ -48,15 +48,30 @@ type metricsResponseWriter struct {
 	http.ResponseWriter
 	statusCode   int
 	bytesWritten int
+	wroteHeader  bool
 }
 
 func (w *metricsResponseWriter) WriteHeader(statusCode int) {
+	if w.wroteHeader {
+		return
+	}
+	w.wroteHeader = true
 	w.statusCode = statusCode
 	w.ResponseWriter.WriteHeader(statusCode)
 }
 
 func (w *metricsResponseWriter) Write(b []byte) (int, error) {
+	if !w.wroteHeader {
+		w.wroteHeader = true
+		w.statusCode = http.StatusOK
+	}
 	n, err := w.ResponseWriter.Write(b)
 	w.bytesWritten += n
 	return n, err
 }
+
+func (w *metricsResponseWriter) Flush() {
+	if flusher, ok := w.ResponseWriter.(http.Flusher); ok {
+		flusher.Flush()
+	}
+}