Streamline certificate authentication

[dopplershift]

It would be helpful to make authenticating to restricted TDS instances (like from ESGF) simpler. This could be used to try to script up access to CMIP5 data:

I was able to generate a certificate using the following syntax in terminal;

myproxyclient logon -b true -T true -s pcmdi.llnl.gov -l jsimkins2 -o ~/creds.pem

with the python package myproxyclient and other directions found here.

Although I was able to generate the certificate, the ESGF server didn't accept it. I tried the methods in the link above but was unsuccessful. After working with the scientists from ESGF, it seems as if the Certificate Authentication authority wouldn't accept the certificates generated by any user and this problem exists on their end to my knowledge. This was about a month ago so perhaps things have changed now that I brought this to their attention. It would be fantastic if Siphon could be used to access guarded datasets like CMIP5. I hope this gives you an idea of how far I got with the issue and hopefully Siphon can carry the torch from here.

My intention with getting this to work is to create a download function that can extract CMIP5 outputs for a single grid point using OPeNDAP/THREDDS. Hopefully there is a way around the token based authentication.