public static App__c ParseRequest(RestRequest req) {
    App__c app = new App__c();
    String body = req.requestBody.toString();
    app = (App__c)JSON.deserialize(body, App__c.class);
    return app;  
}

@HttpPost
global static Id doPost() 
{
    RestRequest req = RestContext.request;        
    App__c app = ParseRequest(req);
    insert app;
    return app.id;
}

public static void postCallout() {

    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;

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

    Obj__c obj = [SELECT Name, Description__c, Skills__c
                       FROM Obj__c WHERE Name = 'Object'];

    HttpResponse response = ourHttp.send(request);      
    OAuth2 objAuthenticationInfo = (OAuth2)JSON.deserialize(response.getbody(), OAuth2.class);
    System.debug('BODY: ' + response.getBody());

    if(objAuthenticationInfo.ACCESS_TOKEN != null){

        JSONGenerator gen = JSON.createGenerator(true);    
        gen.writeStartObject();
        gen.writeStringField('title', obj.Name);
        gen.writeStringField('description', obj.Description__c);
        gen.writeStringField('skills', obj.Skills__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.URL + '/services/apexrest/AppEndpoint');
        HttpResponse finalResponse = finalHttp.send(finalRequest);
        System.debug('RESPONSE BODY: '+ finalResponse.getBody());
    }
}

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