Jenkins Eggplant Runner Plugin 0.0.1.301.v963cffe8ddb_8 and earlier sets the Java system property jdk.http.auth.tunneling.disabledSchemes to an empty value, disabling a protection mechanism of the Java runtime.
The product initializes or sets a resource with a default that is intended to be changed by the administrator, but the default is not secure.
Developers often choose default values that leave the product as open and easy to use as possible out-of-the-box, under the assumption that the administrator can (or should) change the default value. However, this ease-of-use comes at a cost when the default is insecure and the administrator does not change it.