When connecting with a URI and providing a "gssapiServiceName" in the URI, the value never gets used. This is because after the url_parser sets the property `gssapiServiceName` in the options, it gets converted to all lower case afterwards and thus mongodb-core always gets undefined when grabbing the property.

This is the line that the property access always returns undefined and thus results in the service name being set to "mongodb": https://github.com/mongodb-js/mongodb-core/blob/b553ee17e7377b4943af29ce0847598a246ed6f2/lib/auth/gssapi.js#L49

At this line the property has been already converted to lowercase: https://github.com/mongodb/node-mongodb-native/blob/master/lib/authenticate.js#L66 (see my screen shot for the options object at that point)

In the url_parser the value is not all lower case: https://github.com/mongodb/node-mongodb-native/blob/master/lib/url_parser.js#L464