public static void postCalloutResponseContents() {
Settings__c settings = [SELECT ConsumerKey__c, ClientSecret__c, Username__c, Password__c, SecurityToken__c
                        FROM Settings__c
                        WHERE Name = 'OurSettings'];

String consumerKey = settings.ConsumerKey__c;
String consumerSecret = settings.ClientSecret__c;
String username = settings.Username__c;
String password = settings.Password__c + settings.SecurityToken__c;
String request = 'grant_type=password&client_id=' + consumerKey +'&client_secret=' + consumerSecret +
                 '&username=' + username + '&password='+password;

Http ourHttp = new Http();
HttpRequest ourRequest = new HttpRequest();
ourRequest.setBody(request);
ourRequest.setMethod('POST');
ourRequest.setEndpoint(System.Label.Job_Advertisement_URL + '/services/oauth2/token');

Position__c pos = [SELECT Name, Description__c FROM Position__c WHERE Name = 'Title22'];

HttpResponse response = ourHttp.send(ourRequest);
OAuth2 objAuthenticationInfo = (OAuth2)JSON.deserialize(response.getbody(), OAuth2.class);

if(objAuthenticationInfo.ACCESS_TOKEN != null){

    JSONGenerator gen = JSON.createGenerator(true);
    gen.writeStartObject();
    gen.writeStringField('title', pos.Name);
    gen.writeStringField('description', pos.Job_Description__c);
    String jsonString = gen.getAsString();
    System.debug('jsonMaterials: ' + jsonString);

    Http finalHttp = new Http();
    HttpRequest finalRequest = new HttpRequest();

    finalRequest.setHeader('Authorization','Bearer '+ objAuthenticationInfo.ACCESS_TOKEN);
    finalRequest.setHeader('Content-Type','application/json');
    finalRequest.setHeader('accept','application/json');
    finalRequest.setBody(jsonString);

    finalRequest.setMethod('POST');
    finalRequest.setEndpoint(System.Label.Job_Advertisement_URL + '/services/apexrest/jobAdvertisementShow');
    HttpResponse finalResponse = finalHttp.send(finalRequest);
    System.debug('RESPONSE BODY: '+ finalResponse.getBody());
}
}

public class OAuth2{
    public String ACCESS_TOKEN{get;set;}
}

@HttpPost
global static Job__c postJob(String title, String description){
    Job__c thisJob = new Job__c(
        Title__c = title,
        Description__c = description
        );

    try{
        insert thisJob;
    } catch(Exception e){
        System.debug('Error: ' + e.getMessage());
    }
    return thisJob;
}

@HttpPost
global static void myRESTMethod(Map<String, String> mapOfValues) {

    String value;
    for(String key : mapOfValues.keySet()) {
        value = mapOfValues.get(key);
        //  all my other code
        .....
    }
    // all my other code
    ....
}

{
    "mapOfValues" : {
                "key1" : "Value for key1",
                "key2" : "Value for key2",
                "key3" : "Value for key3"
            }
}