fix: assert jwks is present for private_key_jwk first

lib/helpers/client.js

@@ -27,24 +27,24 @@ async function clientAssertion(endpoint, payload) {
     return jose.JWS.sign(payload, key, { alg, typ: 'JWT' });
   }
 
+  const keystore = instance(this).get('keystore');
+
+  if (!keystore) {
+    throw new TypeError('no client jwks provided for signing a client assertion with');
+  }
+
   if (!alg) {
     const algs = new Set();
 
-    instance(this).get('keystore').all().forEach((key) => {
+    keystore.all().forEach((key) => {
       key.algorithms('sign').forEach(Set.prototype.add.bind(algs));
     });
 
     const supported = this.issuer[`${endpoint}_endpoint_auth_signing_alg_values_supported`];
     alg = Array.isArray(supported) && supported.find((signAlg) => algs.has(signAlg));
   }
 
-  const keystore = instance(this).get('keystore');
-
-  if (!keystore) {
-    throw new TypeError('no client jwks provided for signing a client assertion with');
-  }
-
-  const key = instance(this).get('keystore').get({ alg, use: 'sig' });
+  const key = keystore.get({ alg, use: 'sig' });
   if (!key) {
     throw new TypeError(`no key found in client jwks to sign a client assertion with using alg ${alg}`);
   }