Note that the 'input' value could be almost anything, there is a
huge variety of inputs that can work such as 4326, projstrings,
WKT2 strings, EPSG declarations 'EPSG:4326', or common strings like
'WGS84' or 'NAD27'.
Strings like '+init=epsg:4326' have been deprecated but still
can work, so beware.