I figured out the auth endpoint for getting a token. It's not https://auth.euipo.europa.eu/oidc/accessToken, it's https://euipo.europa.eu/cas-server-webapp/oidc/accessToken . So you were using the wrong endpoint. The website doesn't say it, but I got it from their API java file on their website at https://dev.euipo.europa.eu/product/trademark-search_100/api/trademark-search#/Trademarksearch_100/overview .