get https://app.asana.com/api/1.0/custom_fields/
Get the complete definition of a custom field’s metadata.
Since custom fields can be defined for one of a number of types, and
these types have different data and behaviors, there are fields that are
relevant to a particular type. For instance, as noted above, enum_options
is only relevant for the enum type and defines the set of choices that
the enum could represent. The examples below show some of these
type-specific custom field definitions.