Currently, mod_auth_tkt supports also SHA256 and SHA 512 , not just plain MD5. Quoting:
----v---- The default is MD5, which is faster, but has now been shown to be vulnerable to collision attacks. Such attacks are not directly applicable to mod_auth_tkt, which primarily relies on the security of the shared secret rather than the strength of the hashing scheme. More paranoid users will probably prefer to use one of the SHA digest types, however.
The default is likely to change in a future version, so setting the digest type explicitly is encouraged. ----^----
Thus, enable it also in this implementation so one can optionally switch to a stronger secure hash.
Backward compatibility should be untouched as ``md`` is being passed as a default kwarg. The only change affecting external world is a new parameter required at ``calculate digest`` (specifying the digest to use), but as it has probably no use outside the module, this is a non-issue. Alternatively: another optional kwarg.