Support for access to restricted data using credentials

[chad-earthscope]

Restricted data is accessible at the DMC and likely other data centers using credentials (username/password). ROVER should support this mode of access.

The credentials should be used with both the availability and dataselect services.

The credentials should be fetched from a file that could potentially contain credentials for more than one data center. This is in anticipation of ROVER supporting federated access across data centers.

[timronan]

Could we make fields in the rover.config file where credentials would be supplied? One field would accept a list of usernames and the other field would accept a list of passwords. The index would match the user names and passwords. Both fields would be blank upon configuration initialization and would only be valid if an argument was supplied.

[chad-earthscope]

We also need to have data centers listed for each entry, so that is three lists that need to be aligned. Honestly, doing them in separate arrays is kludgey; imagine if you have 4 sets of credentials. It risks non-perfect typing getting it wrong and sending the wrong credentials to the wrong data center.

It would be better to be able to repeat a line that contains <network>:<username>:<password>, so many of them can be specified.

I still would prefer to have a separate file though. We have other tools that will need this capability and it would be good for it to be a common format.