Using a custom authority provider within eosjs for Greymass Fuel

authorityprovider.js

// A custom cosigner AuthorityProvider for EOSJS v2
// This provider overrides the checks on all keys,
// allowing a partially signed transaction to be
// broadcast to the API node.
class CosignAuthorityProvider {
  async getRequiredKeys(args) {
    const { transaction } = args;
    // Iterate over the actions and authorizations
    transaction.actions.forEach((action, ti) => {
      action.authorization.forEach((auth, ai) => {
        // If the authorization matches the expected cosigner
        // then remove it from the transaction while checking
        // for what public keys are required
        if (
          auth.actor === 'greymassfuel'
          && auth.permission === 'cosign'
        ) {
          delete transaction.actions[ti].authorization.splice(ai, 1)
        }
      })
    });
    return convertLegacyPublicKeys((await rpc.fetch('/v1/chain/get_required_keys', {
      transaction,
      available_keys: args.availableKeys,
    })).required_keys);
  }
}

// Pass in new authorityProvider
const api = new Api({
  authorityProvider: new CosignAuthorityProvider(),
  // the rest of your configuration
});

Hi @aaroncox I have exactly the same issue, Did you find the way to solve it??