[ARPE1]

Sí, así lo tenemos pero no hay manera.

Código Delphi [-]
   ... 
    wXML := 'prueba.xsig';
    wURL := 'https://tbai-prep.egoitza.gipuzkoa.eus/WAS/HACI/HTBRecepcionFacturasWEB/rest/recepcionFacturas/alta';
    idhttp1.Request.ContentType := 'application/xml; charset=utf-8';
    IdHTTP1.Request.BasicAuthentication := False;
    wCer := 'CERT_TEST.pfx';
    IdSSLIOHandlerSocketOpenSSL1.SSLOptions.CertFile := wCer;
    IdSSLIOHandlerSocketOpenSSL1.SSLOptions.KeyFile  := wCer;

    IdSSLIOHandlerSocketOpenSSL1.SSLOptions.Mode   := sslmClient;
    IdSSLIOHandlerSocketOpenSSL1.SSLOptions.Method := sslvTLSv1_2; // sslvSSLv23; //sslvTLSv1_1;
    wML.Position := 0;
    Try
      IdHTTP1.Post(wURL, wXML, wMR);
      wMR.Position := 0;
      memo1.Lines.LoadFromStream(wMR, TEncoding.UTF8);
      label1.Caption := IntToStr(IdHTTP1.Response.ResponseCode) + ': ' + IdHTTP1.Response.ResponseText;
    Except
      On E:Exception do
        memo1.Lines.Add(E.Message);
    End;

Gracias por la respuesta.