Using Named Credentials with an endpoint running on my machine

Question

I am trying to generate a JSON Web Token(JWT) via named credentials as per user. I want to use this named creds for authentication purpose. So that using them after salesforce providing JSON web token, in exchange my local auth server will provide a token.

Below are the settings I have added while creating the named credentials as per user.

Label : TestJWTCredential

Name : TestJWTCredential

URL : -> external-endpoint <-

In Authentication Part

Certificate : MulesoftJWT

Identity Type : Per User

Authentication Protocol : JWT Token Exchange

Token Endpoint Url : http://localhost:8091/api/provider/token

Scope : refresh_token full

Issuer : -> my-username <-

Per User Subject : $userId

Audience : http://localhost:8091/api/provider/token

Token Valid for : 1 Hours

JWT Signing Certificate : MulesoftJWT

Ref :- https://help.salesforce.com/articleView?err=1&id=sf.named_credentials_about.htm&type=5#language-combobox

"http://localhost:8091/api/provider/token" This is the url of my authorization server which is a mule application deployed on my local.

Also while calling this named creds from developer console, it gives this error System.CalloutException: Unable to complete the JWT token exchange. Below is the APEX code,

HttpRequest req = new HttpRequest();
req.setEndpoint('callout:TestJWTCredential/services/oauth2/userinfo');
req.setMethod('GET');
req.setHeader('Authorization', 'Bearer'+ UserInfo.getSessionId());
Http http = new Http();
System.debug('REQUEST :::: ' + req);
HTTPResponse resp = http.send(req);
System.debug('RESPONSE  :::: ' + resp.getBody());

Can any body help me how to do it.