public class GoogleOrderPubSubQueueable implements Queueable, Database.AllowsCallouts {
    
    public List<Order> orderList; 
    
    public GoogleOrderPubSubQueueable(List<Order> order){
        this.orderList=order;  
    }
    
    public void execute(QueueableContext context) {
    
    //GCP Authentication
    GCPAuthManagementService gms = new GCPAuthManagementService();
    GCP_Key__mdt serviceAccount = gms.getGCPServiceAccount('Salesforce_PubSub_Orders');

    GCPAuthManagementService.GoogleAuthResponse gmsg = new GCPAuthManagementService.GoogleAuthResponse();
    gmsg = gms.getGCPAuthToken(serviceAccount);
   
    
    String selectFields = serviceAccount.query_fields__c;
    List<String> fields = selectFields.split(',');

    String sobType = serviceAccount.object__c;

    JSONGenerator gen = JSON.createGenerator(true);
    gen.writeStartObject();     
    gen.writeFieldName('records');
    gen.writeStartArray();
    for (SObject sob : Database.query(''
        + ' select ' + String.join(fields, ',')                         
        + ' from ' + sobType
        + ' where id IN: orderList'
        )) {
        gen.writeStartObject();        
        for (String field : fields) {
        Object value = sob.get(field);
        // if no value returned, exclude from JSON
        if (value != null) gen.writeStringField(field, String.valueOf(value));
        }
        gen.writeEndObject();
    }
    gen.writeEndArray();
    gen.writeEndObject();
    String body = gen.getAsString();
    System.debug('body-' + body);
    
    // send order to google pubsub as message
    HttpRequest req = new HttpRequest();
    req.setEndpoint(serviceAccount.audience__c);
    req.setHeader('Content-Type', 'application/json');
    req.setHeader('Authorization', 'Bearer ' + gmsg.id_token);
    req.setMethod('POST');
    req.setbody(body);

    Http http = new Http();
    HTTPResponse response = http.send(req);

    system.debug('HTTP Request: ' + req);
    system.debug('HTTP Response: ' + response.getBody());    
       
        
    }
}