curl --request GET \
  --url http://{host}:{port}/{contextPath}/decision-definition/key/{key}/tenant-id/{tenant-id}/xml \
  --header 'Authorization: Basic <encoded-value>'

{
  "id": "aDecisionDefinitionId",
  "dmnXml": "<?xml version=\"1.0\" encoding=\"UTF-8\"?>\n                                    <definitions xmlns=\"http://www.omg.org/spec/DMN/20151101/dmn.xsd\"\n                                                 id=\"definitions\"\n                                                 name=\"camunda\"\n                                                 namespace=\"http://camunda.org/schema/1.0/dmn\">\n                                      <decision id=\"testDecision\" name=\"decision\">\n                                        <decisionTable id=\"table\">\n                                          <output id=\"result\" name=\"result\" >\n                                          </output>\n                                          <rule id=\"rule\">\n                                            <outputEntry id=\"output1\">\n                                              <text>\"not okay\"</text>\n                                            </outputEntry>\n                                          </rule>\n                                        </decisionTable>\n                                      </decision>\n                                    </definitions>"
}