New tl_data type

[Greg Hudson]

On Wed, 2011-08-31 at 16:54 -0400, Linus Nordberg wrote:
> Now I'm wondering if this should be replaced this with something more
> general.  Greg mentioned a tl_data type with <string>:<string> at some
> point.

This is my preferred option (just string:string; Kerberos doesn't deal
in JSON currently).  This plan has the value of being applicable to
other preauth plugins, and not requiring us to decide what specific OTP
metadata is required within the 1.10 release timeframe.

Another option is to add kadmin support in 1.10 specifically for OTP
metadata; this might be more focused code, but does require us to nail
down what we want the OTP metadata to be.