The administrator of a system should be able to specify a service principal other than the one formed by combining "mongodb" and the FQDN of the host name running the mongo service, as returned by getHostNameCached(). Implementing this feature would facilitate running mongo clusters in environments where servers and clients may disagree about each others' FQDN.

Mongod should start the following two setParameters at startup:

*saslServiceName – reported name of the service for authentication purposes, defaults to mongodb
*saslHostName – reported host name for authentication purposes, defaults to getHostNameCached().

Then, either isMaster should return those parameters, or (better?) the getParameter command should enable even unauthenticated users to fetch those two parameter values.