"request" used the "qs" query string manipulation package and exposed its options in the requestOptions object. One of these, the "arrayFormat" setting, supported a variety of formats for an array parameter { a: [ "b", "c"] }
'indices' a[0]=b&a[1]=c (the default)
'brackets' a[]=b&a[]=c
'repeat' a=b&a=c
'comma' a=b,c

With the switch to cross-fetch this flexibility was lost, as query parameters are handled by resolver_builder code that only implements the first format.