This JsonWebKey does not support the 'sign' operation.

[digitalrbnz]

I am attempting to sign using RSA/PS512 and am getting this error when running the build() function.

[ERROR:flutter/runtime/dart_vm_initializer.cc(41)] Unhandled Exception: Bad state: This JsonWebKey does not support the 'sign' operation.
#0 JsonWebKey._assertCanDo (package:jose/src/jwk.dart:410:7)
jwk.dart:410
#1 JsonWebKey.sign (package:jose/src/jwk.dart:271:5)
jwk.dart:271
#2 new _JwsRecipient._sign (package:jose/src/jws.dart:159:16)
jws.dart:159
#3 JsonWebSignatureBuilder.build. (package:jose/src/jws.dart:193:28)
jws.dart:193
#4 MappedListIterable.elementAt (dart:_internal/iterable.dart:425:31)
iterable.dart:425
#5 ListIterator.moveNext (dart:_internal/iterable.dart:354:26)
iterable.dart:354
#6 new _GrowableList._ofEfficientLengthIterable (dart:core-patch/growable_array.dart:189:27)
growable_array.dart:189
#7 new _GrowableList.of (dart:core-patch/growable_array.dart:150:28)
growable_array.dart:150
#8 new List.of (dart:core-patch/array_patch.dart:39:18)
array_patch.dart:39
#9 ListIterable.toList (dart:_internal/iterable.dart:224:7)
iterable.dart:224
#10 JsonWebSignatureBuilder.build (package:jose/src/jws.dart:195:8)

Example code below

   // create a builder, decoding the JWT in a JWS, so using a
    // JsonWebSignatureBuilder
    var builder = new Jose.JsonWebSignatureBuilder();

    // set the content
    builder.jsonContent = claims.toJson();

    // add a key to sign, can only add one for JWT
    builder.addRecipient(
        new Jose.JsonWebKey.fromJson(
            {"kty": "RSA", 'k":privateKey}),
        algorithm: "PS512");

    // build the jws
    var jws = builder.build();