title: oidc-client-js double encoding acr_values?
body: <p>I'm using oidc-client-js in an Angular application and would like to use the acr_values to pass an IDP value to Identity Server 4. (Identity Server is our primary token service, but we have configured it to use Okta as an external provider for one tenant of the application.)</p>
  <p>Setting the value like this in Angular:</p>
  <pre><code>this.userManager = new UserManager({
        authority: environment.stsAuthority,
        client_id: window.location.hostname,
        acr_values: 'ipd:oktatest',
        ...
  </code></pre>
  <p>The generated URL contains <code>%26acr_values%3Dipd%253Aoktatest</code>   which is what you get if you URL encode <em>idp:oktatest</em> twice.</p>
  <p>If I manually change the URL to <code>%26acr_values%3Didp%3Aoktatest</code> it works as expected. (It's hard to pick up on the difference but the % sign in <em>%3A</em> between <em>ipd</em> and <em>okta</em> becomes <em>%25</em> when it's double encoded.)</p>
  <p>Am I doing something wrong? Is this a bug? Is there a better way to specify the value of acr_values in the Angular code?</p>