A looong time ago PostgreSQL used libssl so I could use it in my extension. (pg_bignum). I remember there being a discussion of switching to gnutls years ago but I don't know what became of it, or if a third approach is now being taken.
Is there an extension-developer-friendly place to start to see the current (security-related) libraries that are always present, that may be used, and which should not be used? (The latter would be due to known conflicts, etc.)
I've been thinking about extending some of my earlier work and know I'll need to use pl/java for some things. However some other things would be better in C, e.g., FDW wrappers for certain types of files.