title: UseJwtBearerAuthentication signing key
body: <p>I'm trying to implement the JWT Bearer Authentication in my AspNetCore MVC app (Web API only) using the JwtBearerMiddleware but am getting a <code>401</code> response with header:</p>
  
  <pre><code>WWW-Authenticate: Bearer error="invalid_token", error_description="The signature key was not found"
  </code></pre>
  
  <p>The relevant code in Startup.cs looks like this:</p>
  
  <pre><code>app.UseJwtBearerAuthentication(new JwtBearerOptions
  {
      Authority = "https://example.okta.com",
      Audience = "myClientId"
  });
  </code></pre>
  
  <p>With the Authority URL I'd expect the middleware to query my Identity Provider metadata from <code>https://example.okta.com/.well-known/openid-configuration</code> to get the <code>jwks_uri</code> to then get the signature keys from <code>https://example.okta.com/oauth2/v1/keys</code>. I don't think this is happening. What do I need to do to get it to find and use the signature keys? Thanks</p>