if (customer.thisOrg.domain_override__c!=null) {
        req.setEndpoint(customer.thisOrg.domain_override__c+'/services/oauth2/token');
    }
    else {
        //check to see if type is sandbox or production/developer
        if(customer.thisOrg.type__c == 'Sandbox'){
            req.setEndpoint('https://test.salesforce.com/services/oauth2/token');
        }
        else{
            req.setEndpoint('https://login.salesforce.com/services/oauth2/token');
        }   
    }
    req.setMethod('POST');
    req.setBody('grant_type=password'+
        '&client_id='+' CLIENT_ID'+
        '&client_secret='+'CLIENT_SECRET'+
        '&username='+customer.thisOrg.username__c+
        '&password='+customer.thisOrg.password__c
    );

    httpResponse res = new httpResponse();

    try {
        // send request     
        Http http = new Http();
        // capture response
        res = http.send(req);
        system.debug('authentication response: '+ res.getBody());
    }
    catch (exception e) {
        system.debug('error authenticating with customer: '+ e.getMessage());
        customer.log += 'nn error authenticating: ' + e.getMessage(); 
          return null;
    }