I landed in your post a bit late. A case was submitted to me recently using OAUTH 1.0 with hmacsha256 and I could have used your solution pretty quickly. I opted for a python embedded method using oauthlib.

Anyway, great work!

Some utility class was missing from your submitted code (SungardK12.Utilities) but nothing we can't figure out.

Why such a complicated question, I wonder. Can anyone answer immediately the "Best Tool" for any given job (other than a salesman, of course)?

I'm a fan of writing my own SQL commands on the SQL Browser (it gives me a sense of power that comes from using the raw tools some deity provided for me) but hey, if it's as simple as editing a bunch of records, well my choice is Dbeaver Community Edition (through JDBC) but it's not the only one based on java (that's why JDBC driver is needed). The one I downloaded came with its own OpenJDK (but it's not full java as some .dll, .dylib or .so libraries are included). It seems you can even install it as some Eclipse plugin if you want! I haven't tested this one yet though.

Well it's simple and you can use the jar that's in the <instance-dir>/dev/java/lib/JDK11/intersystems-jdbc-<version>.jar. It offers to download one as you establish your first connection to an "InterSystems IRIS" or "Cache" database, check this Dbeaver officially supports ....

It has a nice "view data" for a table and allows to edit in a grid (you have to "save" in order to trigger all the UPDATE commands necessary or see them prior to submitting/saving). It's filterable so you see just a range of data you want to edit as in "ID between 40 and 50". If you have some primary key (other than the ID column which is hidden to the beaver but you still can use it to filter data) then the updates will use it no questions asked, otherwise you can use all the columns for the updates but you know how that can have unwanted repercussions. 

It also has the usual import and export (using csv files with mapped columns, just don't use any identity columns!) and the community edition is supposed to be under an apache license. If you really like of course you can buy some license that gives you a full load of functionalities but if it's just to edit some records,  I'd stick to the community edition.