Uses of the abbreviation "auth." in an academic paper?

Writing a “mock” academic paper for a writing project.
Can’t seem to find a good source for the basic conventions of use.
I.e., can “auth.” be used solely to denote the perspective of the source, or of the person writing the paper which cites said source?
As one example, is it acceptable common practice to use the abbreviation in the following way:
”(which substance of necessity ____; auth.) does not belong to (etc.)”
—where the quotes denote the total of the sourced section, and the parenthetical insertion a summary of a much longer portion.
Or is it more common to use ‘auth.’ in parentheses, at the end of a quote if you have already quoted the same author earlier on?
I realize this information should be out there somewhere, but I couldn’t really find anything saying “do this”, and “don’t do that”, or even really presenting many examples of the use of this abbreviation (without, I guess, digging through enough books and research papers on my own to get the idea) hence my curiosity. Thanks.