func extractMetadataFromReq(ctx context.Context, r *http.Request) (metadata map[string]string, err error) {
	return extractMetadata(ctx, textproto.MIMEHeader(r.Form), textproto.MIMEHeader(r.Header))
}

func extractMetadata(ctx context.Context, mimesHeader ...textproto.MIMEHeader) (metadata map[string]string, err error) {
	metadata = make(map[string]string)

	for _, hdr := range mimesHeader {
		// Extract all query values.

pkg net/http, type Cookie struct, SameSite SameSite
pkg net/http, type SameSite int
pkg net/http, type Transport struct, MaxConnsPerHost int
pkg net/http/httptrace, type ClientTrace struct, Got1xxResponse func(int, textproto.MIMEHeader) error
pkg net/http/httptrace, type ClientTrace struct, WroteHeaderField func(string, []string)
pkg net/http/httputil, type ReverseProxy struct, ErrorHandler func(http.ResponseWriter, *http.Request, error)