Revert "fix: encode client_secret_basic - _ . ! ~ * ' ( ) characters"

This reverts commit 5a2ea80, even
though it is the correct implementation some of the most widely used
identity providers don't follow the specification.

lib/helpers/client.js

@@ -9,26 +9,7 @@ const request = require('./request');
 const { keystores } = require('./weak_cache');
 const merge = require('./merge');
 
-function formUrlEncode(token) {
-  return encodeURIComponent(token).replace(/(?:[-_.!~*'()]|%20)/g, (substring) => {
-    switch (substring) {
-      case '-':
-      case '_':
-      case '.':
-      case '!':
-      case '~':
-      case '*':
-      case "'":
-      case '(':
-      case ')':
-        return `%${substring.charCodeAt(0).toString(16).toUpperCase()}`;
-      case '%20':
-        return '+';
-      default:
-        throw new Error();
-    }
-  });
-}
+const formUrlEncode = (value) => encodeURIComponent(value).replace(/%20/g, '+');
 
 async function clientAssertion(endpoint, payload) {
   let alg = this[`${endpoint}_endpoint_auth_signing_alg`];

test/client/client_instance.test.js

@@ -2274,7 +2274,7 @@ describe('Client', () => {
         expect(await clientInternal.authFor.call(client, 'token')).to.eql({
           headers: {
             Authorization:
-              'Basic YW4lM0FpZGVudGlmaWVyOnNvbWUrc2VjdXJlKyUyNitub24lMkRzdGFuZGFyZCtzZWNyZXQ=',
+              'Basic YW4lM0FpZGVudGlmaWVyOnNvbWUrc2VjdXJlKyUyNitub24tc3RhbmRhcmQrc2VjcmV0',
           },
         });
       });