"Sources and methods" seems to be an official NSA terminology to talk about the main categories things that whistleblowers were not supposed to whistleblow.
It came to Ciro Santilli's attention in the Reality film about Reality Winner, and are words she apparently used extensively and which are quoted e.g. at www.theguardian.com/us-news/2022/jul/25/reality-winner-leaked-file-on-russia-election-hacking-because-public-was-being-lied-to
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