On https://www.wageningenalumniportal.nl/en/home/Pages/home.aspx you can register, fill in your e-mail address and create your password. The website also provides a link to "Alumni Service", which gives an overview of services that are offered to Wageningen University alumni.
Source: https://www.wageningenalumniportal.nl/en/home/Pages/home.aspx
