migration from LPRng: filtering lpd metadata

[Richard Brittain]

We have linux systems migrating from LPRng to CUPS (RHEL) and a printing
system that must be accessed via lpd.  It requires some changes in the
job metadata (specifically the username) to fulfill authorization
requirements, and I can't see any hooks in CUPS for changing that.
LPRng has a filter specifically for munging the metadata (as opposed
to the file content), which was perfect for this purpose.

It looks like I could modify the lpd backend fairly easily to achieve
this, or create a new backend with a different URI method that does
the same thing but if there is a place in the existing CUPS filter
conventions to drop this in, I'd rather do that.  It looks like the lpd
backend will take a 'customized' username on the command line if one is
provided.

Many thanks for any help.

 Richard