Salesforce Named Credentials

dev
1

I am currently using following apex code to check if the user exists in discourse.

HttpRequest req3 = new HttpRequest();
req3.setEndpoint('https://forumname/admin/users/list/all.json?&email=' + emailaddress);
req3.setMethod('GET');
req3.setHeader('api-username','myusername');
req3.setHeader('api-key','myapikey');

Http http3 = new Http();
HTTPResponse res3 = new HTTPResponse();

if (Test.isRunningTest() && (mock!=null)) {
res3 = mock.respond(req3);
} else {
res3= http3.send(req3);
} 

System.debug(res3.getBody().length());
if(res3.getBody().length()==2)
    System.debug('Discourse Not found');
else 
{
    System.debug(res3.getBody());
    System.debug('Discourse found ');   
    Discourse=true;
}

How do I set up the named credentials so that I remove the username/key from this code ?