[PROJ] How to match a proj string to the db?

[Nyall Dawson]

Hi list

Still fighting with transitioning QGIS to proj 6. (Honestly, I wonder
if this task will ever end...!)

If I have a proj string (say +proj=longlat +datum=WGS84 +no_defs
+type=crs), how can I match this back to an authority/code from proj's
db?

proj_identify doesn't seem to be capable of this (maybe by design? The
dox say: "This is implemented for GeodeticCRS, ProjectedCRS,
VerticalCRS and CompoundCRS"). The dox for proj_identify also have a
cryptic note "The candidate CRSs are either hard-coded, or looked in
the database when authorityFactory is not null." What exactly does
this mean? I can't see where authorityFactory is specified, or a hard
coded list of candidates is specified either... Is this outdated
documentation?

Nyall