There is a section that reads:
You may experience an error “400 BAD REQUEST We cannot log in user because the HTTP request doesn't contain a valid SAML response.” This means that there is a missing signature in the SAML communication. Upon your request, our support team can skip the signature check on GoodData’s side so that you are able to move forward. If you wish to skip the signature check, please reach out to support@gooddata.com. If nothing else helps, please reach out to our support and they should be able to help!